As someone who designed hard drive controllers when this tech was new, you are right - FM, MFM and RLL are all RLL. However, the quality of the oxide needs to be a whole lot better for "RLL" to work well. Formatting needs to write new address marks (which begin sector marks and data). Sector marks are a bunch of data which tells you which sector will come next (ie contains the track number and sector number). However - the address marks and sector data may be interleaved - sector label 1 is followed by data for the last sector, then sector label two, then sector data one! This is because the formatter processor may not be fast enough to figure out which label it just read in the inter-sector gap! I warn you - address marks are a possible problem: Mostly people used the IBM address mark. Unfortunately the IBM documents were wrong! The data bits were defined in chronological order, but the clock bits in reverse chronological order. I designed a controller with the clock bits in the correct order (as an option). Using the bits in the correct order means that the address mark contains a single flux transition in between two gaps exceeding the max legal distance in legit data. This means it is a unique pattern on the drive surface. The industry standard version is illegal as data, but is not necessarily unique. Using my address mark, most drives had enormously fewer bad sectors and read errors - but were not compatible with formatters made by IBM, Western Digital etc. I used programmable logic (which was new at the time) to map data into RLL code . In addition to formatters for mainframes, I also did the first hard drive interface for the Apple ][, and one for the BBC micro. Both used the 6502 CPU - like Woz did for the floppy controller!
Wow! Fantastic to hear! For what it's worth, I've tested every single drive in my collection (over 500+ drives at this point) as RLL and I've had very few drives fail RLL that didn't already have issues during nominal MFM operation.
I always though RLL was a kind of extension to MFM. a 20MB MFM drive would be 30MB with RLL, IIRC. What I can't recall are the specific debug commands used for the low level formatting.
Sure, hundreds of us neckbeards were shouting SYS C: at the telly (or even FORMAT /S), but, and this is important, hundreds more didn't have the first clue so it's excellent that you're showing this to the inexperienced :D
That's part of why I love watching people work on very different old tech. Man's got an incredible handle on the minicomputers like the Centurion, but DOS isn't really in his wheelhouse, where I can breeze through DOS but I'm *absolutely* lost on the big(gish) iron.
I was taught this stuff back in school; but, having not touched it in over 20 years, the actual command was foggy. More reason to check back at this stuff periodically, I guess.
Before MS-DOS 4, the sys command required the disk to be freshly-formatted. Starting with MS-DOS 4, the sys command was able to handle files already being on the disk.
I think the root cause is in a boot sector loader. In 3.3 it was just loading system from reserved sectors. Later it started to look for system in directory entries
@@big0bad0brad They are reserved once used. So it's more them being fixed ones, and if they already are in use for other things, sys cannot free (and reserve) them.
@@alexloktionoff6833 The DR-DOS bootloader could read the system files from the directory entries, which was very convenient. However, MS-DOS was never able to do this.
You've low-level formatted the ST4097 with the drive parameters of the ST238R, so you'll only have 30MB usable. On these older controllers you have to select the drive parameters with jumpers. They depend on the Controller's BIOS ROM version though. There are lists online of which ROM version supports which drives. It's quite possible that your ROM won't support the correct parameters, so you'd either have to modify it and change the parameter table, or get the WD SuperBios which can be configured to any drive parameters. The ST4097 is a 80MB MFM drive, so with 2,7 RLL it should give you roughly 120MB!
FYI, an ST238R is simply an ST225 that passed a few more QC checks. Quite a few hobbyists with ST225s plugged in an RLL board and got the 32MB capacity with no issues.
When my NYC government agency bought a lot of Priam brand hard drives they sent me to Priam training in NYC around 1986 where we learned about RLL (2,7) encoding. I hadn’t thought about that for almost 40 years and your video brought it all back to me. I remember listening to Howard Stern on the radio on the way to the hotel in Queens where they held the class. You explained the concept well.
Ok.. the moment he mentioned Procomm Plus, a wave of nostalgia hit me like an ocean breeze.. All the BBS i've spent time on came back to me.. lol That is just awesome!
Oh, memory lane !!! Thanks for the video. One thing about the MFM vs RLL thing that you missed (not because you were wrong) is that those differences came along because of software, not hardware. People started noticing that there were better ways of encoding things, hence the LZW algorithm that gave us ZIP and DCT (Discreet Cosine Transform) that gave us JPEG. That is where this magical way of encoding stuff came from, if you encode it like that, you are able to compress more stuff together, both being able to store more as well as being able to read/write faster. Once again, Thanks for the video.
Correct, Seagate drives format depends on controller (especially early controllers). I had IBM PC XT clone at work and controller and HDD was treated always as bonded pair in terms of swapping between machines. MFM controllers have some own specific sector prefixes and coding quirks (interleaving sectors).
The way RLL works is quite different from LZW or Huffman tables or any of that, although these ideas were used for "disk doubling" software. 2,7-RLL actually writes twice as many bits as MFM, but by strictly limiting how many consecutive 0s or consecutive 1s are allowed, it can pack those bits in three times as tight and still work with them reliably. These are mapped through a simple lookup table to convert to/from data bytes, resulting in a net 50% increase in both storage and speed, all invisible to the OS. All DOS/BIOS know is that the disk has 26 sectors per track instead of 17.
I did a similar thing in the early 90s. I got two MFM hard drives (one full height and one half height) basically for free, as there were considered old, loud, large and slow by then. I learned about RLL and that using that would make the storage capacity some 50% more and reading the drives would be faster. I was happy to have the extra storage, and my tower case has enough slots for the huge disks. But man, were those drives noisy...
I know a lot about the ST-225 / ST-238 , rotation speed stability was the difference as RLL needed better control . The ST-238 is a ST-225 that passed testing . The ST-238 is sutable with modifications for video image file of one digitized with ( PWM on disk ) NTSC frame per track a quiet revolution at that era : )
Oh man that took me back 30+ years to playing around with my Amstrad PC1512 and then PC1640 machines. Formatting hard drives, swapping floppies back n forth, trying out copy commands, learning about Autexec.Bat, Config.Sys, XCopy, editing files, trying and failing, then trying and succeeding etc etc. What amazing days they were 🥰
It's just because there is no separate timing signal, and the oscillator/clock with the disk writer and disk reader won't be synchronized. A device called a phased-lock-loop is an oscillator where you feed back the received signal into it to force the local oscillator to drift into alignment with a signal and when the signal drops out (or when there is a gap with no transitions) the local oscillator in the PLL will keep on ticking as long as not too much time passes before a new transition to re-synchronize. This allows the signal to contain several similar bits crammed together which represents no transition. Other ways to do this without a PLL would be to have start and stop bits like serial but that would be unideal.
It also has to do with the nature of magnetic media. Ideally, if the media had response down to DC, we could save an ordinary serial stream on it similar to RS-232. But, magnetic media can only return a signal on changes to flux, so a steady state of the same bit quickly collapses to no output at all, essentially acting as a high-pass filter. Run Length (RL) refers to the amount of time (in clocks) that we can stay in a state between flux transitions reliably. So, we have to re-encode the bits such that the signal sent to the media remains within a certain frequency band regardless of the data we're representing by introducing extra flux transitions according to some formula. FM does this in a more intuitive way, but GCR is more optimized for density.
@@bryede This is true also for radio signals, because the automatic gain control will attenuate the signal if there is a constant amplitude. But for signals like QAM, there is always a constant clock signal to avoid having to stuff transitions by using code.
You could also think of FM as a serial format with 1 data bit and 0 stop bits. You don't necessarily need a fancy PLL to decode FM. I once built a data separator for a 1791-based floppy controller out of a 4-bit counter and a gate or two. It just reset the counter on every flux transition. Probably a bit too crude for professional use, but it worked fine!
A couple things. 1) You should copy all the dos files to a dos directory and the procom plus files into a procomm directory. There is a limit to the number of files you can have in the root directory. I forget exactly what it is, but it isn't that much and it's probably less for dos 3. It will generate false disk full errors if that number is met. Second, you should probably create a config sys file and an autoexec bat file with a decent files= statement and load ansi sys (both in config sys) and a path statement in the autoexec bat and a prompt=$p$G for a normal looking c prompt.
The max number of directory entries for FAT12 and FAT16 seems to depend on the total size of the disk. For smaller removable disks it's typically only 100-200 entries. I think hard disks were still limited to 512 entries though. FAT32 got around this by storing the root directory _after_ the FAT along with the rest of the data on the disk and could grow dynamically after the disk was formatted (compare to FAT12 and FAT16 which stored the root directory before the FAT and so was fixed in size when formatting).
Yes, I was squirming at the copying of *everything* to root, but then again it is a limited-purpose computer at the moment (the HDD effectively being a much faster floppy). But a simple autoexec.bat that directly loads Procomm could be useful (for the current usage). I expect the original HDD would have had a startup/utilities menu at boot.
@@SenileOtaku Yes. Often it was a simply type statement with a bunch of lines saying press 1 plus enter to start procomm plus Press 2 plus enter to start bla blah blah With a 1 and 2 and 3.... bat files that end by cls, cd back to root and then a type statement displaying the menu again. Very simple, very effective. A lot of the early XT machines didn't include 640k. So having a menu loaded into memory wasn't really ideal.
I think the limit for files in the root is 512. In any case, putting things in their own directories makes it easier to find things! I think you get a message like Directory Full if you try to exceed this, as opposed to Disk Full if the disk is actually full.
Instead of using format c: and sys c: you can also use format /s c: and transfer the system files as part of the format. Also, ensure that the partition you want to boot is active. From what I recall fdisk from dos 3.3 will take care of that, but it is something to always check.
and if you know the drive is good, add /q for a quick format. The non-quick version just checks for bad sectors before writing the file system. Not sure if that is already in this old version of MS DOS, but for sure in later systems.
@@drstefankrank I'm not entirely sure which version introduced /q but it wasn't available yet in 3.3. From memory it was 5.0, but.. I try to forget DOS 4.0, so it might have been that one as well.
@@c128stuff Like 4th Edition D&D vs. 5e, there were some good ideas in DOS 4 but for the most part they got carried over into version 5 so there's no reason to stick with 4 and its warts.
@@mal2ksc I was a tester for DOS 4, and DOS 4 fdisk actually has a little bit of code from me (fix for selecting an other disk than the primary one). It certainly had some good ideas, but it was rather problematic due to memory use. I probably spent hundreds, if not thousands of hours on helping IBM 'large accounts' (ie, large corporate customers) dealing with exactly that issue. (when DOS 4.01 got released, I worked for IBM) DOS 5 was a huge improvement, containing all the improvements from DOS 4, but without the issues.
Those older Western Digital controllers have jumpers to set the drive type. Since you originally had a ST-238R in there, it's treating the ST-4097 as a ST-238R which means it formatted it with 615 cylinders, 4 heads, and 27 sectors. The drive types are defined in the ROM on the controller itself and it probably doesn't support the ST-4097 at all. There is a utility called SpeedStor that has a command line switch to display the drive types supported by the controller. Later WD controllers offered a free format option where you could enter in the correct drive parameters for the drive. The drive interleave is how the sectors are laid down onto the drive during the low-level format. A 4 to 1 interleave will skip every four sectors. The reason for this, is the 8-bit controller is not fast enough to process an interleave ratio lower then 4 to 1. I you were to tell the controller to use an interleave ratio of 3 or lower, you would end up with extremely slow drive performance as the controller would fail to read the next sector in line and have to wait for it come back around to try again. This would result in a 27 to 1 interleave ratio meaning one sector read for each platter revolution. If you were to toss in a 16 bit RLL controller like a ST-21R, you would be able to run a 1 to 1 interleave and should see 7 mb/s drive through put. There is even more tweaks that can be done during a low-level format such as head an cylinder skewing. Which affects how the sectors are positioned on the adjacent platters so when the head switches or moves it doesn't have to wait for an entire platter revolution. Without skewing, a fast drive like the ST-4097 will be faster with a 2 to 1 interleave vs a 1 to 1 interleave. You may also want to check out the ESDI interface which extends on the ST-412 (MFM / RLL) interface. ESDI is not compatible with the older ST-412 interface drives.
ESDI drives differ by having the data separator and PLL electronics in the drive instead of on the backplane controller. ESDI is quite different from ST-506/412 in a number of ways. ESDI supports higher level commands to the drive than ST-506/412 too.
Good explanation of interleave. However in my experience many better controllers I worked with would work down to 2:1 on a XT. Tim Patterson (yes that one) made a “Falcon” controller that was able to use some kind of burst mode on the bus to be able to handle a 1:1 interleave. I’d have one in my old deskpro, but it was MFM only and I wanted RLL for the greater storage.
I had three ESDI drives donated to me with a lot of bad sectors. They were still larger than any other drives I happened to have at the time, both logically (150 and 300MB drives) and physically - these were the full height of 3.2 inches. My drives also took about a minute to come up to a stable speed. Yes, they were on their last legs, however they still made a Linux system viable for me.
@@brickviking667 I had a lot better luck with ESDI drives. I was a bit unnerving to see a label with a big bad sector map, but it was rare to ever experience gown defects. It seemed all or nothing - either the drive worked, or it was a brick.
I remember when I was a kid working with these drives. I had a 20mb MFM drive, a 40mb RLL drive, and later a full-height 80mb RLL drive that I salvaged. It weighed a ton (figuratively). One of the heads had broken off the actuator and was bouncing between two platters, so I messed with jumpers and ended up with 65mb usable -- as three separate partitions. The drive lasted another 6 or 7 years before finally failing catastrophically. When I disassembled the device (after the complete failure), I discovered that the reason my trick worked was because the head that broke was the next-to-last. So when I reset the jumper to reduce the heads by two, it was ignoring the last two, which was where the fault was.
It warms my heart to know that there are still ST-238Rs alive out there in the wild. Not extinct yet! Dave, remember the only reason anyone ran the 238 vs. a 225 was the 50% more capacity (30MB vs. 20MB) at an incrementally higher price. Not sure why EDS would spec a 238R in the machine, I guess they needed the 30MB capacity? Otherwise, the 225s were as common as cigarette butts back in the day.
Man! so many memories came back with this video 1) After removing the screws, the bump that you had to make to the case with the palm. 2) Putting the case back on: You have to make pressure with your hand's palms leaving your fingers free to make an inverse pressure to fit it again. ....Yes, the secuence to format would be: FDISK to read the disk, examine it, chose your partition configuration and after that create partitions. Then Format C:/s /c, being C: for the first hard drive (Select 1? in FDISK) /s to make it bootable (so you can skip Sys C: later) and /c to check for bad sectors.
The sequence is as follows: 1) Low level format: debug g c800:5 to run the BIOS provided on the extension card The sector interleave is the sector count between consecutive sectors on the same track. This value depends on a whole bunch of factors, the most important one being the speed of the CPU. Because of the sector skipping the transfer rate decreases The value of 4 means read one sector skip 3 and read the 4th one etc... For an XT class machine it is probably the right value. 2) Use Fdisk to create 1 Primary dos partition (the only one Dos can boot from) 1 extended partition that will itself contain as many partition as necessary 3) Dos format letter: /u (/u = unconditional do NOT retain previous data structures) The /u switch is only applicable for recent revisions of Dos (5 and up ?) 4) Transfer the system with the 'sys drive:' command From a: with a bootable disk in it run sys c: 5) Copy the rest of the files with copy (or xcopy if available) Putting all dos files under c:\dos is considered good practice Only the 3 system files (see bellow) and boot configuration files (config.sys, autoexec.bat) should be at the root of C: PS: the system files: IBMBIOS.SYS IBMDOS.SYS COMMAND.COM are supposed to be at predefined file allocations positions otherwise the boot process will stall. The sys command does not support "making room" for these files by moving files elsewhere. This is why the sys command has to be applied first, before other file can use up that space. PS2: you might want to give ms-dos 5.x a try to break the 32Mb per partition barrier if the ram size allows.
Since it's not an original IBM-PC, it is probably "IO.SYS" and "MSDOS.SYS" instead. IO.SYS needs to be the first entry in the FAT, starting in the first available sector for data, and contiguous with MSDOS.SYS, which needs to be the second entry in the FAT.
Interleave can be later optimized without a reformat using Spinrite. So yeah, start with a conservative value like 4:1. If it turns out later that your hardware operates well at 3:1, that's basically just an overnight "set it and forget it" changeover. A lot of later RLL controllers, even the 8-bit ISA ones, worked well at 1:1 interleave. So did some of the later MFM controllers. Again, this is something that Spinrite can address if you chose wrong.
The correct way to install DOS would be using SELECT, not using format/sys/copy. You'd create the partition with FDISK, then reboot and run: SELECT A: C:\DOS 001 US It formats the partition, makes it bootable, copies all DOS files into the given path (C:\DOS) and configures it for country code 001 and US keyboard.
Interleave indicated how many sectors should be placed *between* sectors in a given sequence. Why does that matter? Because if you were reading sequential sectors, the processor would take some amount of time to transfer data to the PC. This means if you ordered them [1,2,3,4,5,6,7,8], by time you transferred the data after reading sector 1, the head may be physically over sector 4, or 6; and you'd have to wait for the drive to spin back around the start of sector 2. If you get the offset right (say it was optimally 3 or 4 sectors), then an interleave of4 [at least] would put 4 sectors between each sequential one to get the best response time. That would give you an order like this: [1,3,5,7,2,4,6,8]. This way by time the system is ready to read the next sector, sector 2 is the next one to hit (or the one after, worst case). If it hit a conflict when building the map, it would just push to the next free sector block, and continue that pattern until the sector list was full. Worst case, some end sectors have slightly worse performance, but it' still way better than an interleave of 1 (which is how most early drives were formatted). There was a tool called "spinrite" that would copy out, then low-level at about 20 tracks in with different interleaves to find the best one. It would err toward the larger number, and then re-low-level format the whole drive with that offset. (Later versions would change interleave several times over a larger drive, since the value could change based on track velocity and density.) This would cause at least that first area of the drive to be perfectly interleaved. Since that's where the boot, system, and often the MFT lived, it made the boot sequence, and the entire performance of the filesystem significantly faster when properly tuned. Mind you: some drives did not support this low-level rewriting. Many RLL drives would forbid it, since the read timing was so critical that it couldn't be relied on for that track data to be written out in the field. The equipment needed to do the timing properly was far more expensive, and was only found in the factories that made the drives. By that point though, manufacturers were optimizing interleave anyway before production, and drives started having buffers to optimize the transfer to the system. Some early RLL drives mistakenly left the low-level write code in though, and triggering it would just nuke the entire drive. Guess where your ST241 lands in that! If you guessed "nukeable with spinrite", you'd be correct. I know that one from painful personal experience.
Love that you explained the difference between MFM and RLL ! Love this video, again. I remember going through BYTE Magazine saying "NO/YES" to the HD controllers because I needed an MFM/RLL for the HDD that I wanted to install.
You can run MFM drives on an RLL controller and, back in the day, be very happy getting 50% more space, but there's a cost. As the drives heat up, you can end up getting more and more read errors since the disks aren't really rated for that kind of density. The drive may last a couple years running like this, then the errors start. I ran into this with a couple of ST-225's. Both drives started with read errors about 2 years into their lives. It got to the point where they were so hot, I couldn't touch the drives after 30 minutes. I really had to copy the data off of them, but to keep the drives running cool enough for long enough, I had to run the drives under a towel and a gallon bag of ice water. Worked like a charm!
I did the ST-225 / ST-238 modification back in the mid-80's as well! I do remember the early version of spinrite, to determine the optimal sector interleave (1 = 1,2,3,4; 2 = 1,3,5,...; etc) before reformatting it. it's been so long so i'm not surprised how many people haven't actually experienced the joy of going from 20mb to 30mb on your hard drive!
I agree they are amazing. I imaged a DEC Rainbow disk just in case it fails. The DEC Decmate II disk (same type) is already bad and can't be read. I need to get a few more of these to image the drive in my Pro-350.
You questioned what ‘interleave’ is. The sectors are not placed sequentially on the track, but have one or more sectors before the next sector in sequence (eg, 1,x,y,2,… would be an interleave of 3 (if I’m remembering correctly). This was done when the controller couldn’t keep up with sequentially written sectors, so rather than wait an entire disk rotation, they simply ‘moved’ the next sector a few sectors away to let the controller catch up. Eventually ‘all’ controllers became fast enough and interleave factors became 1:1. Love to watch your videos. A real trip down memory lane. Thanks.
Two thumbs way up for Dave's emulator. When the hard drive on my Kaypro 10 died, I bought one of these. It was close to plug-and-play to install and the old Kaypro restore disks had no problems with it at all!!
Oh man, this reminds me of my qbx days except you are getting hard drives to work. I never fixed a single one, I just got them from the trash working and used them til I found a better system in the trash. I kept trading up and up entire dos systems out of the trash in the 90's until I got up to a 286 processor. I've seen many of those old drives in terrible states of condition making lovely progressive failure noises. I don't miss the 80'88's trying to run QBX with dos 6 on 600k of ram either. HOWEVER I do love magnetic recording and data fundamentals (TAPE) so your video here is functional therapy for me. Thank you, and I enjoy coming along for the ride!
Haha! Love the title of this video :D - There it was, you addressed the title fairly early into the video with a neat explanation. It has surfaced a long buried memory, I'm now trying to think whether I came across these encoding schemes as a student or afterward, lol. At any rate, it's really good to get these "vintage" techniques back in the light of day - thank you, Usagi (and today, AJ)! I'm curious to see what headway you've made with DEC's insanely brilliant PDP-11 power supply schema 😜
You need to copy all the DOS files into a directory usually called "DOS", because the number on entries i.e. files in the root directory is limited. The error message is a bit useless since it will only say something "not enough space left..." when it actually should say "not enough file table entries left..."
It's either that, or old versions of sys weren't able to move stuff around to make space for IO.SYS (of which at least the beginning needs to be in the first sector, IIRC)
@@seritools Ahh yes, that was the reason, I remember now. Similar for Windows: KRNL386.SYS can be anywhere on the drive but must not be moved. It was loaded using a sector table written to the boot sector compiled during installation. If the checksum didn't match then you got "Cannot find or load KRNL386.SYS".
The limit is 512 items in the root directory, which includes hidden files and subdirectory’s. I know this thanks to having to recover a customer’s system after they saved everything to the root…
I used to use MFM drives with a RLL controller back int the 80s without issues to save a bit on the cost of RLL certified drives which were more expensive
It was easy to get bitten if the drive wasn’t up to par. I had to replace the RLL controllers with MFM controllers in a lot of computers equipped with Seagate ST-238 drives owned by an organization I worked for. The Seagate ST-238 drives had a nasty habit of having the rotational speed gradually drop off from the nominal 3600 RPM. MFM controllers can handle the speed inaccuracy, but RLL controllers ran into trouble. There was no obvious way to adjust the ST-238 spindle speed in the field.
@@ChuckvdL I had an IBM PS/2 Model 80 which was lent to me for several months for the purpose of reviewing Micro Channel video cards for a Computer Shopper article. The model 80 was then the flagship PS/2 with, I believe, a 16 MHz 80386 CPU. The 80 meg ESDI drive was labeled IBM, and it didn’t look like any other drives with which I was familiar. I don’t know if IBM made the drive themselves. As you noted, it was not terrible, but much better than a contemporary MFM drive. I also tried a loaner 327 meg CDC ESDI drive (forget the exact model) and the CDC drive was quite a bit faster than the IBM-supplied drive. The CDC unit was quite massive by comparison - both were full height 5.25 inch.
@@wtmayhew omg ‘microchannel’. IBM’s attempt to regain control of cloaning by creating new proprietary standards that they would license…. That was a year or two after the 20 Meg half height ST-225 came out, but IBM drives still sucked. Many were also low level formatted with interleave’s like 5:1 or 6:1. I think because IBM’s controller cards were terrible as well
@@ChuckvdL Yes, Micro Channel was a tactical error. It was well intentioned from an engineering standpoint but needlessly proprietary. VL-bus and then almost immediately PCI made Micro Channel irrelevant.
Funny how I haven't done a lowlevel format of an RLLor MFM drive since the late 80s, but I still remembere debug g=c800:5. Crazy what the brain stashes away. I am loving your channel. It's got so much fantastic content. /spins propellar hat.
Back in the early 90s, I remember connecting an MFM hard drive to an 8-bit ISA Seagate RLL controller and I would get an additional ~30% storage after low-level reformatting the drive. The downside was that I noticed the drive would run hotter. Someone once explained to me it had to do with how it would run the actuator which was out of spec. So yes, I would agree from experience that MFM Is RLL and RLL is RLL.
Idk why but the "technical difficulties" with the piano brake down killed me I wasn't expecting something that random upbeat and fast paced in the middle of all the interesting long winded info
Unlocks some old memories. When I was about 12 in the 90s I got an old hand me down 286 with basically the same version of DOS 3.3 (Although I think it was the IBM branded PC-DOS)
What a fabulous explanation... I've been throwing MFM and RLL around for decades... Now i can throw them around and actually know what I'm talking about. I love the plastic panel on the front of that drive... a half height cosplaying a full height drive. ;)
Finally someone explains the concept behind mfm vs rll. I used mfm drives with rll controllers for such a long time with my Amiga 1000 and (Commodore) PCs until IDE showed up. Why? As kids we recycled broken drives by swapping parts around and used what we got. We basically never had problems with repurposed ST225, ST251 and the full size ones which model number I just forgot, which just worked fine with rll Controllers.
Procom plus has a BBS build into it. It was my first BBS as my dad had procom plus for work. Once I got my BBS going I switched to TriBBS. Back when I had a 8086.. Ah miss those days.
Imagine back in 1985 when Amstrad released the CPC 664, an upgrade over the 464 with a 3 inch floppy drive. Instead of taking 15 minutes for an audio cassette tape to load a game, it would only take a few seconds. Floppy disks were lightning fast!
As far as I remember, these hdds had a seagate software for low level formatting, and they came with a bad sector continuous paper sheet from factory that you had to type when low level formatting. Because they had bad sectors from factory. Then you could proceed to partition and format. but you had to setup the sector cylinder and head spcts in bios first. Don´t know it was done on a XT. I was a kid and saw my dad doing it infinite times.
@ 19:45 - the clacking noise is usually a system-controlled calibrate action, the pattern depends on the BIOS. Later BIOS firmware on different machines simply trusted the disk calibration data (which the controller could read when it was powered on).
In the mid 80s, I saved up to buy a hard drive from "Hard Drives International" for an IBM clone PC. ( I couldn't afford a real IBM PC as it was over $2000 back then). It would be my first hard drive, moving up from "floppy boots", and I was pretty excited. The drive I got was RLL, and somehow, I think the RLL drives were less expensive than MFM, which is why I got the RLL (they were expensive back then). Also, that was the first time I heard of RLL, and never forgot what the acronym stood for, but didn't know the tech behind it :)
For some odd reason, I'm subscribed and enjoy your videos. I don't know what you are doing or understand it, but I have a small appreciation of it from my experience with old Apples, Macs, and PCs I used in my youth. Apple II is the oldest Apple computer I used and Win 3.0 is the oldest PC. My justification for watching your videos is that someday civilization might collapse and maybe my brain is frozen or I will be cloned and reawoken in the future and the only way to access these ancient surviving computers is to pull the knowledge of these videos from my brain. I pop one on and just watch it like an old movie or music while drinking my coffee. p.s. I think the funniest aspect of this is without any clue what's going on, I still pause the video when I go get food or something to drink. It's not like I would notice anything I miss for a few minutes but I hate to hear something interesting happening in the kitchen and have to rewind.
I remember dos 3 all the way through 6.21. Those were the days os ascii, asembly, basic, and 300 baud modems with bbs. When you copied without the sys I knew it wouldn't boot. Some things you never forget like sys and format /s. The coolest thing I ever did with ms-dos 3.2 was change the assembly to say other things. Like RN-BOSS etc. I had the only OS that I customized the message on. It was so easy to edit in the assembly because it was plain text. I could change things like Microsoft to read other words as well. Fun times. Those were the teue hacker days. When the Pink Shirt book came out, every true hacker bought it. That was the ultimate bible for understanding the OS and hard drive storage. If you wanted to write a virus or something that book was gold.
It's been 30 years since I played with RLL drives. I had a 21mb ST225 drive in a 286 running DOS. I do remember it had a clunky, nasty sound when it ran....
MFM, RLL, Voice Coil termos que ficaram para sempre na memória da gente xD FDISK... Debug + G=100 + Entrar lista de Bad Sectors + etc :D fiz muito isso nos computadores, naqueles anos. A gente instalava muitos HD, apesar do preço ser alto. Duas coisas atrapalhavam as controladoras: Mau contato (Mesmo sendo novas) e aterramento. Sim! As fezes, só de colocar um parafuso, mesmo que fechando o gabinete, fazia a controladora ou a placa-mãe ficarem loucas! Vendo a situação, lembrei de um tempo em que alguns conjuntos (controladora+Winchester) ocorria um problema: Após formatar e transferir o sistema e dar boot, dizia que não havia O.S. para dar boot. Daí, tinha que executar o Sys c: novamente. Com o tempo, descobri o que era (não lembro mais). Bem, grato pelo vídeo!
That "insane" list of errors was actually common in late 80's when installing Netware. Can't remember the tool but we always had to run a program (sys?) to warn the os of the bad stuff. Then ages of figuring out if track 0 was reliable and then an age of checking the disk. Later versions could handle bad blocks dynamically shaving days of installing a server.
To format the harddrive and transfer system in one step you can use A>FORMAT C: /S but also to make your system disk look a little nicer you could place the dos files in a subdirectory by itself. A>MD C:\DOS and then copy the diskettes from A -> C:\DOS A>COPY 'star'.'star' C:\DOS (TH-cam won't show the 'star' character) to enable the system to find the dos files at the correct subdir you need to add following line to the AUTOEXEC.BAT file PATH=C:\DOS Maybe other ppl suggested this too, so I'm sorry if this would be a double entry. Very nice machine :)
Usually format C: /Q /Y only write an empty File Allocation Table and does not ask for confirmation. This is time saving not to cycle through writing all the cylinders.
@bubullenoiraude you lived in a dangerous fast way! At company level I cannot afford any errors to show up unexpectedly so format without checking for bad sectors was a big NO, No for me and my work.
17:56 I had an ST4096 back in the day. Looking it up, I see that the difference is that your ST4097 is RLL, as opposed to the original ST4096 which was MFM. Due to this, the higher number of sectors per track gives us the higher transfer rate and capacity.
Thinking way, way back, and with some uncertainty: a handy keyboard thing is the upand down arrow keys. From the command prompt, type UP-arrow and it displays the previous command line. DOS keep a few lines available. Browse through them with UP and DOWN arrows. When you get one you want to repeat, press enter. If you want to edit it, use RIGHT and LEFT arrow keys.
Great! I did lots of FDISKs on MFM and RLL drives way back when. About the interleave factor. This is an offset for reading sectors while the HD spins by. If you select the IF properly the drive doesn't have to take another turn. Formating a system drive was basic knowledge in the early 80ies. The boot sector has to be bootable.
Blast from the past - thank you. I remember in the mid-80's buying a HUGE 72MB Micropolis drive and then RLL'ing it to 144MB. An yes, my piers thought I was insane for wanting that much storage. I won't admit what I paid for that (used!) 72MB 8" drive But I was successful and became "the man of the hour" Thank you for the infoTainment. The check is in the mai! Cheers from So.Ca.USA 3rd House On the Left.
How are you planning to do file transfer? Write an XMODEM program for the Centurion, and then use Procomm+'s file transfer support (which surely includes XMODEM)? I don't understand why different disk block sizes matter if you are backing up at the file level... Flashback to using KERMIT to transfer files from our VAX/VMS mainframe to my Atari ST in 1987ish...
I was wondering the same thing. The serial transfer would act as an abstraction layer, leaving the program on either end to handle any data storage through the OS. Might need something to make a note of any extra attributes the Centurion's filesystem adds to files or translate them to a DOS equivalent, maybe?
@@ForgottenMachines I was a noob once too, it was just very funny watching you guys work with it. Seeing that drive being read though was very awesome, thanks for helping Usagi dump it.
Wow. References to sector interleaving. Haven't seen that sort of thing in a very long time. BTW, IIRC, you can type "format c: /s" to format the drive and make it bootable in one step instead of running sys after running format.
MS-DOS format has several options. Re making the drive bootable, /B reserves space on the drive for the system files so that later you can use the SYS command after files have been copied. /S will copy over the required os files for boot after the format has completed. With this option you don't need to use the SYS command afterwards.
The commonly used low-level formats on magnetic storages actually introduce special encodings in the header of the ID and the data block of each sector. This special encoding wouldn't be possible with strict FM or MFM encoding. For instance, see ECMA 125 section 9.12 and 10.2/10.4. The special A1h byte omits a magnetic transition between two bits where it would be necessary for a strict MFM encoding. The controller can (and needs to) detect this byte anyway, which is giving away that it is an RLL detector in reality.
Sys doesn't need it to be freshly formatted. It needs a very specific place in the drive to be empty to place the system files in that specific location. If that specific space isn't free then you get that error regardless of how much free space the rest of the drive has.
The interleave factor is a way to tune the I/O speed. IThe optimal for 8-bit buses is 3:1 and 16-bit buses as 1:1. But those are best cases and there are caveats. I mean, if you use an 8-bit card on a 16-bit (eg., 80286) bus, and the optimal interleave is 3 for the card on an 8-bit system, 4:1. So the slower the controller, the higher the interleave you need to get the fastest rate you can get with that configuration. And programs like the older Spinrite and Optune can re-interleave the drive on the fly for you. They can test the interleave factor and reformat to the best. And the 2 programs I mentioned let you reformat in place without necessarily needing to back up your data (though you should). And yes, a 20 MB MFM drive (17 SpT) would be a 31 MB RLL drive (26 SpT).
31:30 you could have added a /s after the format command to essentially do both steps at once. Been ages since I used that early of a version of DOS, but I know that worked at least with version 5 and later. Should still work on 3.3 though I believe.
Cool video, i'm actual working on an "WANG Professional Computer" (It is an MS-DOS machine witch is not IBM compatible and use ist own card interface no ISA connectors), with some problems with the comunication with the hard drive. It's an MFM Drive, spins up normally and runs through it's self test and the drives service manual says, when the powerlight stays on (What it does) and doesn't blink, the drive is in ready state. After 1 minute of computer selftesting it says "booting from winchester disk..... failed. After that i couldn't test anymore because the damn RIFAS goes up in smoke. But befor i powered it on, i dumped all the ROMs (safety first).
As someone who designed hard drive controllers when this tech was new, you are right - FM, MFM and RLL are all RLL. However, the quality of the oxide needs to be a whole lot better for "RLL" to work well. Formatting needs to write new address marks (which begin sector marks and data). Sector marks are a bunch of data which tells you which sector will come next (ie contains the track number and sector number). However - the address marks and sector data may be interleaved - sector label 1 is followed by data for the last sector, then sector label two, then sector data one! This is because the formatter processor may not be fast enough to figure out which label it just read in the inter-sector gap!
I warn you - address marks are a possible problem: Mostly people used the IBM address mark. Unfortunately the IBM documents were wrong! The data bits were defined in chronological order, but the clock bits in reverse chronological order. I designed a controller with the clock bits in the correct order (as an option). Using the bits in the correct order means that the address mark contains a single flux transition in between two gaps exceeding the max legal distance in legit data. This means it is a unique pattern on the drive surface. The industry standard version is illegal as data, but is not necessarily unique. Using my address mark, most drives had enormously fewer bad sectors and read errors - but were not compatible with formatters made by IBM, Western Digital etc. I used programmable logic (which was new at the time) to map data into RLL code .
In addition to formatters for mainframes, I also did the first hard drive interface for the Apple ][, and one for the BBC micro. Both used the 6502 CPU - like Woz did for the floppy controller!
Very interesting, I always thought that there must be a trick to write rll adress marks. Do you have a video or link for the details of encoding?
Very interesting!
Wow! Fantastic to hear!
For what it's worth, I've tested every single drive in my collection (over 500+ drives at this point) as RLL and I've had very few drives fail RLL that didn't already have issues during nominal MFM operation.
decoding that raw flux image will be an interesting problem
I always though RLL was a kind of extension to MFM. a 20MB MFM drive would be 30MB with RLL, IIRC. What I can't recall are the specific debug commands used for the low level formatting.
Sure, hundreds of us neckbeards were shouting SYS C: at the telly (or even FORMAT /S), but, and this is important, hundreds more didn't have the first clue so it's excellent that you're showing this to the inexperienced :D
I thought I remembered a shortcut to use the /s parameter for formatting to make it bootable
That's part of why I love watching people work on very different old tech. Man's got an incredible handle on the minicomputers like the Centurion, but DOS isn't really in his wheelhouse, where I can breeze through DOS but I'm *absolutely* lost on the big(gish) iron.
I was taught this stuff back in school; but, having not touched it in over 20 years, the actual command was foggy. More reason to check back at this stuff periodically, I guess.
Format c: /s would have done it
Everyone else living in a rural property in Texas has a "ranch," whereas Dave has a "compound"
Tell that to the Davidians
I'd wager there are a few other compounds, as well as bunkers, installations, strongholds, and camps.
We have enough computing power to land people on the moon (almost at least)! I think that qualifies us as a compound :D
@@UsagiElectric So, a calculator, basically? :P
@@johnpmchappellpixel 7a
Before MS-DOS 4, the sys command required the disk to be freshly-formatted. Starting with MS-DOS 4, the sys command was able to handle files already being on the disk.
I think the root cause is in a boot sector loader. In 3.3 it was just loading system from reserved sectors. Later it started to look for system in directory entries
What you would typically do was use the /s parameter for the FORMAT command, which would do the equivalent of SYS immediately after the format.
@@alexloktionoff6833 If they were reserved sectors, then there would be no problem loading the boot code in later.
@@big0bad0brad They are reserved once used. So it's more them being fixed ones, and if they already are in use for other things, sys cannot free (and reserve) them.
@@alexloktionoff6833 The DR-DOS bootloader could read the system files from the directory entries, which was very convenient. However, MS-DOS was never able to do this.
Yay!
30:47 indeed we were screaming "sys c:". I'm so glad that at LAST I had some relevant knowledge for this channel 🤣
Or "format c: /s"
format c: /s
Was it a later dos version that included "format /s c:"?
I chuckled and just wait to him discover just copying the files don't work hahahaha
I also thought NOOOOOOO you're missing the sys command 🙂
You've low-level formatted the ST4097 with the drive parameters of the ST238R, so you'll only have 30MB usable. On these older controllers you have to select the drive parameters with jumpers. They depend on the Controller's BIOS ROM version though. There are lists online of which ROM version supports which drives. It's quite possible that your ROM won't support the correct parameters, so you'd either have to modify it and change the parameter table, or get the WD SuperBios which can be configured to any drive parameters.
The ST4097 is a 80MB MFM drive, so with 2,7 RLL it should give you roughly 120MB!
I like the part where they make sure that the SD card is mounted and then writing the raw image to the onboard storage. 😂
I saw that as well and waited for the part where they pull the SD Card and wonder why it is empty upon inspection on a PC, but it never happened.
@@drstefankrank And then you hope very perfusely that the root partition isn't a ramdisk.
@@Stoney3K I also didn't pay too much attention on how big the root is and expected a disk full error, but it seems it has plenty of space.
@@drstefankrank I expected the disk full error any moment.
Well, when dealing with critical, non-replacable data, it's probably better to save to internal storage and then copy to the SD.
Brings back memories of my first PC in 1988, running Debug to low level format a 5MB Rodime HDD I bought second hand.
I remember those Rodime drives. Davong Systems drives too.
Wow there's a brand name I forgot about. Remember doing the same thing. Was always a white knuckle experience.
FYI, an ST238R is simply an ST225 that passed a few more QC checks. Quite a few hobbyists with ST225s plugged in an RLL board and got the 32MB capacity with no issues.
36:02 You're welcome, it and it WAS an absolutely blast!
When my NYC government agency bought a lot of Priam brand hard drives they sent me to Priam training in NYC around 1986 where we learned about RLL (2,7) encoding. I hadn’t thought about that for almost 40 years and your video brought it all back to me. I remember listening to Howard Stern on the radio on the way to the hotel in Queens where they held the class. You explained the concept well.
Ok.. the moment he mentioned Procomm Plus, a wave of nostalgia hit me like an ocean breeze.. All the BBS i've spent time on came back to me.. lol That is just awesome!
Yes, I also used Procomm quite a bit back in those wonderful BBS days. Also ran my own BBS for many years. I wish I had kept a backup of it.
But did you pay for it?
Likewise
@@JanBruunAndersen Did anyone? wasn't it shareware....
@@paulstubbs7678 - it was. Which meant that after a trial period you were supposed to pay for it.
Oh, memory lane !!! Thanks for the video. One thing about the MFM vs RLL thing that you missed (not because you were wrong) is that those differences came along because of software, not hardware. People started noticing that there were better ways of encoding things, hence the LZW algorithm that gave us ZIP and DCT (Discreet Cosine Transform) that gave us JPEG. That is where this magical way of encoding stuff came from, if you encode it like that, you are able to compress more stuff together, both being able to store more as well as being able to read/write faster. Once again, Thanks for the video.
Correct, Seagate drives format depends on controller (especially early controllers). I had IBM PC XT clone at work and controller and HDD was treated always as bonded pair in terms of swapping between machines. MFM controllers have some own specific sector prefixes and coding quirks (interleaving sectors).
The way RLL works is quite different from LZW or Huffman tables or any of that, although these ideas were used for "disk doubling" software. 2,7-RLL actually writes twice as many bits as MFM, but by strictly limiting how many consecutive 0s or consecutive 1s are allowed, it can pack those bits in three times as tight and still work with them reliably. These are mapped through a simple lookup table to convert to/from data bytes, resulting in a net 50% increase in both storage and speed, all invisible to the OS. All DOS/BIOS know is that the disk has 26 sectors per track instead of 17.
@@mal2kscIf there's a lookup table involved, would that be a really early form of a static dictionary?
I did a similar thing in the early 90s. I got two MFM hard drives (one full height and one half height) basically for free, as there were considered old, loud, large and slow by then. I learned about RLL and that using that would make the storage capacity some 50% more and reading the drives would be faster. I was happy to have the extra storage, and my tower case has enough slots for the huge disks. But man, were those drives noisy...
I know a lot about the ST-225 / ST-238 , rotation speed stability was the difference as RLL needed better control . The ST-238 is a ST-225 that passed testing .
The ST-238 is sutable with modifications for video image file of one digitized with ( PWM on disk ) NTSC frame per track a quiet revolution at that era : )
All Hail Ross Perot! (that noise is the sound of our souls being sucked out by the floppy)
So that was the "giant sucking sound"...
Oh man that took me back 30+ years to playing around with my Amstrad PC1512 and then PC1640 machines. Formatting hard drives, swapping floppies back n forth, trying out copy commands, learning about Autexec.Bat, Config.Sys, XCopy, editing files, trying and failing, then trying and succeeding etc etc. What amazing days they were 🥰
I was 6yo when I played with those things, I can't believe that was 30y ago , time flies.
It's just because there is no separate timing signal, and the oscillator/clock with the disk writer and disk reader won't be synchronized. A device called a phased-lock-loop is an oscillator where you feed back the received signal into it to force the local oscillator to drift into alignment with a signal and when the signal drops out (or when there is a gap with no transitions) the local oscillator in the PLL will keep on ticking as long as not too much time passes before a new transition to re-synchronize. This allows the signal to contain several similar bits crammed together which represents no transition. Other ways to do this without a PLL would be to have start and stop bits like serial but that would be unideal.
It also has to do with the nature of magnetic media. Ideally, if the media had response down to DC, we could save an ordinary serial stream on it similar to RS-232. But, magnetic media can only return a signal on changes to flux, so a steady state of the same bit quickly collapses to no output at all, essentially acting as a high-pass filter. Run Length (RL) refers to the amount of time (in clocks) that we can stay in a state between flux transitions reliably. So, we have to re-encode the bits such that the signal sent to the media remains within a certain frequency band regardless of the data we're representing by introducing extra flux transitions according to some formula. FM does this in a more intuitive way, but GCR is more optimized for density.
@@bryede This is true also for radio signals, because the automatic gain control will attenuate the signal if there is a constant amplitude. But for signals like QAM, there is always a constant clock signal to avoid having to stuff transitions by using code.
You could also think of FM as a serial format with 1 data bit and 0 stop bits.
You don't necessarily need a fancy PLL to decode FM. I once built a data separator for a 1791-based floppy controller out of a 4-bit counter and a gate or two. It just reset the counter on every flux transition. Probably a bit too crude for professional use, but it worked fine!
As an old EDS'er I smile when I see that logo.
A couple things. 1) You should copy all the dos files to a dos directory and the procom plus files into a procomm directory. There is a limit to the number of files you can have in the root directory. I forget exactly what it is, but it isn't that much and it's probably less for dos 3. It will generate false disk full errors if that number is met.
Second, you should probably create a config sys file and an autoexec bat file with a decent files= statement and load ansi sys (both in config sys) and a path statement in the autoexec bat and a prompt=$p$G for a normal looking c prompt.
Yeah i was thinking that, he got spoiled by the Centurion 🙂 IIRC it just says no free space when there is or that abort retry ignore prompt.
The max number of directory entries for FAT12 and FAT16 seems to depend on the total size of the disk. For smaller removable disks it's typically only 100-200 entries. I think hard disks were still limited to 512 entries though. FAT32 got around this by storing the root directory _after_ the FAT along with the rest of the data on the disk and could grow dynamically after the disk was formatted (compare to FAT12 and FAT16 which stored the root directory before the FAT and so was fixed in size when formatting).
Yes, I was squirming at the copying of *everything* to root, but then again it is a limited-purpose computer at the moment (the HDD effectively being a much faster floppy). But a simple autoexec.bat that directly loads Procomm could be useful (for the current usage).
I expect the original HDD would have had a startup/utilities menu at boot.
@@SenileOtaku Yes. Often it was a simply type statement with a bunch of lines saying
press 1 plus enter to start procomm plus
Press 2 plus enter to start bla blah blah
With a 1 and 2 and 3.... bat files that end by cls, cd back to root and then a type statement displaying the menu again. Very simple, very effective.
A lot of the early XT machines didn't include 640k. So having a menu loaded into memory wasn't really ideal.
I think the limit for files in the root is 512. In any case, putting things in their own directories makes it easier to find things! I think you get a message like Directory Full if you try to exceed this, as opposed to Disk Full if the disk is actually full.
Instead of using format c: and sys c: you can also use format /s c: and transfer the system files as part of the format.
Also, ensure that the partition you want to boot is active. From what I recall fdisk from dos 3.3 will take care of that, but it is something to always check.
and if you know the drive is good, add /q for a quick format. The non-quick version just checks for bad sectors before writing the file system. Not sure if that is already in this old version of MS DOS, but for sure in later systems.
I came here to say this, but I wasn't sure if /s was available in 3.3. It's been a very long time! lol
@@drstefankrank I'm not entirely sure which version introduced /q but it wasn't available yet in 3.3. From memory it was 5.0, but.. I try to forget DOS 4.0, so it might have been that one as well.
@@c128stuff Like 4th Edition D&D vs. 5e, there were some good ideas in DOS 4 but for the most part they got carried over into version 5 so there's no reason to stick with 4 and its warts.
@@mal2ksc I was a tester for DOS 4, and DOS 4 fdisk actually has a little bit of code from me (fix for selecting an other disk than the primary one).
It certainly had some good ideas, but it was rather problematic due to memory use.
I probably spent hundreds, if not thousands of hours on helping IBM 'large accounts' (ie, large corporate customers) dealing with exactly that issue.
(when DOS 4.01 got released, I worked for IBM)
DOS 5 was a huge improvement, containing all the improvements from DOS 4, but without the issues.
Lol, I just knew AJ from Knight Rider Historians. I had no idea he was into vintage computing.
LOL SAME!!! funny how worlds collide. Though I guess AJ is the one who is reverse engineering/rebuilding a lot of the vintage electronics in the Cars.
@@Nebula1701 Yes, it's true! Not just the cars, but reverse engineering a vintage computer was the key for us finding the Semi!
Those older Western Digital controllers have jumpers to set the drive type. Since you originally had a ST-238R in there, it's treating the ST-4097 as a ST-238R which means it formatted it with 615 cylinders, 4 heads, and 27 sectors. The drive types are defined in the ROM on the controller itself and it probably doesn't support the ST-4097 at all. There is a utility called SpeedStor that has a command line switch to display the drive types supported by the controller. Later WD controllers offered a free format option where you could enter in the correct drive parameters for the drive. The drive interleave is how the sectors are laid down onto the drive during the low-level format. A 4 to 1 interleave will skip every four sectors. The reason for this, is the 8-bit controller is not fast enough to process an interleave ratio lower then 4 to 1. I you were to tell the controller to use an interleave ratio of 3 or lower, you would end up with extremely slow drive performance as the controller would fail to read the next sector in line and have to wait for it come back around to try again. This would result in a 27 to 1 interleave ratio meaning one sector read for each platter revolution. If you were to toss in a 16 bit RLL controller like a ST-21R, you would be able to run a 1 to 1 interleave and should see 7 mb/s drive through put. There is even more tweaks that can be done during a low-level format such as head an cylinder skewing. Which affects how the sectors are positioned on the adjacent platters so when the head switches or moves it doesn't have to wait for an entire platter revolution. Without skewing, a fast drive like the ST-4097 will be faster with a 2 to 1 interleave vs a 1 to 1 interleave. You may also want to check out the ESDI interface which extends on the ST-412 (MFM / RLL) interface. ESDI is not compatible with the older ST-412 interface drives.
ESDI drives differ by having the data separator and PLL electronics in the drive instead of on the backplane controller. ESDI is quite different from ST-506/412 in a number of ways. ESDI supports higher level commands to the drive than ST-506/412 too.
Good explanation of interleave.
However in my experience many better controllers I worked with would work down to 2:1 on a XT. Tim Patterson (yes that one) made a “Falcon” controller that was able to use some kind of burst mode on the bus to be able to handle a 1:1 interleave. I’d have one in my old deskpro, but it was MFM only and I wanted RLL for the greater storage.
I had three ESDI drives donated to me with a lot of bad sectors. They were still larger than any other drives I happened to have at the time, both logically (150 and 300MB drives) and physically - these were the full height of 3.2 inches. My drives also took about a minute to come up to a stable speed. Yes, they were on their last legs, however they still made a Linux system viable for me.
@@brickviking667 I had a lot better luck with ESDI drives. I was a bit unnerving to see a label with a big bad sector map, but it was rare to ever experience gown defects. It seemed all or nothing - either the drive worked, or it was a brick.
I remember when I was a kid working with these drives. I had a 20mb MFM drive, a 40mb RLL drive, and later a full-height 80mb RLL drive that I salvaged. It weighed a ton (figuratively). One of the heads had broken off the actuator and was bouncing between two platters, so I messed with jumpers and ended up with 65mb usable -- as three separate partitions. The drive lasted another 6 or 7 years before finally failing catastrophically. When I disassembled the device (after the complete failure), I discovered that the reason my trick worked was because the head that broke was the next-to-last. So when I reset the jumper to reduce the heads by two, it was ignoring the last two, which was where the fault was.
It warms my heart to know that there are still ST-238Rs alive out there in the wild. Not extinct yet!
Dave, remember the only reason anyone ran the 238 vs. a 225 was the 50% more capacity (30MB vs. 20MB) at an incrementally higher price. Not sure why EDS would spec a 238R in the machine, I guess they needed the 30MB capacity? Otherwise, the 225s were as common as cigarette butts back in the day.
Man! so many memories came back with this video 1) After removing the screws, the bump that you had to make to the case with the palm. 2) Putting the case back on: You have to make pressure with your hand's palms leaving your fingers free to make an inverse pressure to fit it again. ....Yes, the secuence to format would be: FDISK to read the disk, examine it, chose your partition configuration and after that create partitions. Then Format C:/s /c, being C: for the first hard drive (Select 1? in FDISK) /s to make it bootable (so you can skip Sys C: later) and /c to check for bad sectors.
The sequence is as follows:
1) Low level format:
debug g c800:5 to run the BIOS provided on the extension card
The sector interleave is the sector count between consecutive sectors on the same track.
This value depends on a whole bunch of factors, the most important one being the speed of the CPU.
Because of the sector skipping the transfer rate decreases
The value of 4 means read one sector skip 3 and read the 4th one etc... For an XT class machine it is probably the right value.
2) Use Fdisk to create 1 Primary dos partition (the only one Dos can boot from)
1 extended partition that will itself contain as many partition as necessary
3) Dos format letter: /u (/u = unconditional do NOT retain previous data structures)
The /u switch is only applicable for recent revisions of Dos (5 and up ?)
4) Transfer the system with the 'sys drive:' command
From a: with a bootable disk in it run sys c:
5) Copy the rest of the files with copy (or xcopy if available)
Putting all dos files under c:\dos is considered good practice
Only the 3 system files (see bellow) and boot configuration files (config.sys, autoexec.bat) should be at the root of C:
PS: the system files:
IBMBIOS.SYS
IBMDOS.SYS
COMMAND.COM
are supposed to be at predefined file allocations positions otherwise the boot process will stall.
The sys command does not support "making room" for these files by moving files elsewhere.
This is why the sys command has to be applied first, before other file can use up that space.
PS2: you might want to give ms-dos 5.x a try to break the 32Mb per partition barrier if the ram size allows.
Since it's not an original IBM-PC, it is probably "IO.SYS" and "MSDOS.SYS" instead. IO.SYS needs to be the first entry in the FAT, starting in the first available sector for data, and contiguous with MSDOS.SYS, which needs to be the second entry in the FAT.
You can omit the SYS command if you do format /s
That works too.
Interleave can be later optimized without a reformat using Spinrite. So yeah, start with a conservative value like 4:1. If it turns out later that your hardware operates well at 3:1, that's basically just an overnight "set it and forget it" changeover.
A lot of later RLL controllers, even the 8-bit ISA ones, worked well at 1:1 interleave. So did some of the later MFM controllers. Again, this is something that Spinrite can address if you chose wrong.
The correct way to install DOS would be using SELECT, not using format/sys/copy.
You'd create the partition with FDISK, then reboot and run:
SELECT A: C:\DOS 001 US
It formats the partition, makes it bootable, copies all DOS files into the given path (C:\DOS) and configures it for country code 001 and US keyboard.
@@kpanic23 Is that similar to Setup or Install in newer DOS versions?
Interleave indicated how many sectors should be placed *between* sectors in a given sequence. Why does that matter? Because if you were reading sequential sectors, the processor would take some amount of time to transfer data to the PC. This means if you ordered them [1,2,3,4,5,6,7,8], by time you transferred the data after reading sector 1, the head may be physically over sector 4, or 6; and you'd have to wait for the drive to spin back around the start of sector 2. If you get the offset right (say it was optimally 3 or 4 sectors), then an interleave of4 [at least] would put 4 sectors between each sequential one to get the best response time. That would give you an order like this: [1,3,5,7,2,4,6,8]. This way by time the system is ready to read the next sector, sector 2 is the next one to hit (or the one after, worst case). If it hit a conflict when building the map, it would just push to the next free sector block, and continue that pattern until the sector list was full. Worst case, some end sectors have slightly worse performance, but it' still way better than an interleave of 1 (which is how most early drives were formatted).
There was a tool called "spinrite" that would copy out, then low-level at about 20 tracks in with different interleaves to find the best one. It would err toward the larger number, and then re-low-level format the whole drive with that offset. (Later versions would change interleave several times over a larger drive, since the value could change based on track velocity and density.) This would cause at least that first area of the drive to be perfectly interleaved. Since that's where the boot, system, and often the MFT lived, it made the boot sequence, and the entire performance of the filesystem significantly faster when properly tuned.
Mind you: some drives did not support this low-level rewriting. Many RLL drives would forbid it, since the read timing was so critical that it couldn't be relied on for that track data to be written out in the field. The equipment needed to do the timing properly was far more expensive, and was only found in the factories that made the drives. By that point though, manufacturers were optimizing interleave anyway before production, and drives started having buffers to optimize the transfer to the system. Some early RLL drives mistakenly left the low-level write code in though, and triggering it would just nuke the entire drive. Guess where your ST241 lands in that! If you guessed "nukeable with spinrite", you'd be correct. I know that one from painful personal experience.
Love that you explained the difference between MFM and RLL ! Love this video, again. I remember going through BYTE Magazine saying "NO/YES" to the HD controllers because I needed an MFM/RLL for the HDD that I wanted to install.
You have a great knack for simplifying and explaining all of the tech jargon. Extremely fun entertaining and educational channel.
You can run MFM drives on an RLL controller and, back in the day, be very happy getting 50% more space, but there's a cost. As the drives heat up, you can end up getting more and more read errors since the disks aren't really rated for that kind of density. The drive may last a couple years running like this, then the errors start. I ran into this with a couple of ST-225's. Both drives started with read errors about 2 years into their lives. It got to the point where they were so hot, I couldn't touch the drives after 30 minutes.
I really had to copy the data off of them, but to keep the drives running cool enough for long enough, I had to run the drives under a towel and a gallon bag of ice water. Worked like a charm!
I did the ST-225 / ST-238 modification back in the mid-80's as well! I do remember the early version of spinrite, to determine the optimal sector interleave (1 = 1,2,3,4; 2 = 1,3,5,...; etc) before reformatting it. it's been so long so i'm not surprised how many people haven't actually experienced the joy of going from 20mb to 30mb on your hard drive!
David’s MFM emulator’s are awesome!!! I have maybe 8 of them!!! Truly amazing MFM solution!!!
I agree they are amazing. I imaged a DEC Rainbow disk just in case it fails. The DEC Decmate II disk (same type) is already bad and can't be read. I need to get a few more of these to image the drive in my Pro-350.
You questioned what ‘interleave’ is. The sectors are not placed sequentially on the track, but have one or more sectors before the next sector in sequence (eg, 1,x,y,2,… would be an interleave of 3 (if I’m remembering correctly). This was done when the controller couldn’t keep up with sequentially written sectors, so rather than wait an entire disk rotation, they simply ‘moved’ the next sector a few sectors away to let the controller catch up. Eventually ‘all’ controllers became fast enough and interleave factors became 1:1. Love to watch your videos. A real trip down memory lane. Thanks.
Two thumbs way up for Dave's emulator. When the hard drive on my Kaypro 10 died, I bought one of these. It was close to plug-and-play to install and the old Kaypro restore disks had no problems with it at all!!
I'd give more than 2 thumbs up if I had more thumbs. I imaged my DEC Rainbow disk just in case as it's an ST-251 I believe.
Oh man, this reminds me of my qbx days except you are getting hard drives to work. I never fixed a single one, I just got them from the trash working and used them til I found a better system in the trash. I kept trading up and up entire dos systems out of the trash in the 90's until I got up to a 286 processor. I've seen many of those old drives in terrible states of condition making lovely progressive failure noises. I don't miss the 80'88's trying to run QBX with dos 6 on 600k of ram either.
HOWEVER I do love magnetic recording and data fundamentals (TAPE) so your video here is functional therapy for me. Thank you, and I enjoy coming along for the ride!
In my old 286 system I had a Seagate ST238R HDD controller. I ran several different MFM drives as RLL with absolutely zero problems.
Brings back memories
a:\format c: /sys
is a shortcut to put system files onto new boot drive in a single line when formatting
Just /s is all you need but yes, pretty much. 🙂
Love the B-W Corsiar-2 photo print on the wall. Great show... thank you.
Haha! Love the title of this video :D - There it was, you addressed the title fairly early into the video with a neat explanation. It has surfaced a long buried memory, I'm now trying to think whether I came across these encoding schemes as a student or afterward, lol.
At any rate, it's really good to get these "vintage" techniques back in the light of day - thank you, Usagi (and today, AJ)!
I'm curious to see what headway you've made with DEC's insanely brilliant PDP-11 power supply schema 😜
You need to copy all the DOS files into a directory usually called "DOS", because the number on entries i.e. files in the root directory is limited. The error message is a bit useless since it will only say something "not enough space left..." when it actually should say "not enough file table entries left..."
It's either that, or old versions of sys weren't able to move stuff around to make space for IO.SYS (of which at least the beginning needs to be in the first sector, IIRC)
@@seritools Ahh yes, that was the reason, I remember now. Similar for Windows: KRNL386.SYS can be anywhere on the drive but must not be moved. It was loaded using a sector table written to the boot sector compiled during installation. If the checksum didn't match then you got "Cannot find or load KRNL386.SYS".
The limit is 512 items in the root directory, which includes hidden files and subdirectory’s. I know this thanks to having to recover a customer’s system after they saved everything to the root…
I used to use MFM drives with a RLL controller back int the 80s without issues to save a bit on the cost of RLL certified drives which were more expensive
It was easy to get bitten if the drive wasn’t up to par. I had to replace the RLL controllers with MFM controllers in a lot of computers equipped with Seagate ST-238 drives owned by an organization I worked for. The Seagate ST-238 drives had a nasty habit of having the rotational speed gradually drop off from the nominal 3600 RPM. MFM controllers can handle the speed inaccuracy, but RLL controllers ran into trouble. There was no obvious way to adjust the ST-238 spindle speed in the field.
@@wtmayhewthey weren’t very good drives, but they were better than anything IBM was putting in XT’s and AT’s.
@@ChuckvdL I had an IBM PS/2 Model 80 which was lent to me for several months for the purpose of reviewing Micro Channel video cards for a Computer Shopper article. The model 80 was then the flagship PS/2 with, I believe, a 16 MHz 80386 CPU. The 80 meg ESDI drive was labeled IBM, and it didn’t look like any other drives with which I was familiar. I don’t know if IBM made the drive themselves. As you noted, it was not terrible, but much better than a contemporary MFM drive. I also tried a loaner 327 meg CDC ESDI drive (forget the exact model) and the CDC drive was quite a bit faster than the IBM-supplied drive. The CDC unit was quite massive by comparison - both were full height 5.25 inch.
@@wtmayhew omg ‘microchannel’. IBM’s attempt to regain control of cloaning by creating new proprietary standards that they would license….
That was a year or two after the 20 Meg half height ST-225 came out, but IBM drives still sucked. Many were also low level formatted with interleave’s like 5:1 or 6:1. I think because IBM’s controller cards were terrible as well
@@ChuckvdL Yes, Micro Channel was a tactical error. It was well intentioned from an engineering standpoint but needlessly proprietary. VL-bus and then almost immediately PCI made Micro Channel irrelevant.
Data recovery specialists! Nice work :)
HI KERI,.lol,. how r u ? this is really interesting,. its like the toddler years of computers,.lol
Congratulations! This entire system is coming together nicely!
Funny how I haven't done a lowlevel format of an RLLor MFM drive since the late 80s, but I still remembere debug g=c800:5. Crazy what the brain stashes away.
I am loving your channel. It's got so much fantastic content. /spins propellar hat.
I like this AJ guy! good sense of humour. I love how the software reports runtime with nanosecond resolution :)
Back in the early 90s, I remember connecting an MFM hard drive to an 8-bit ISA Seagate RLL controller and I would get an additional ~30% storage after low-level reformatting the drive.
The downside was that I noticed the drive would run hotter. Someone once explained to me it had to do with how it would run the actuator which was out of spec.
So yes, I would agree from experience that MFM Is RLL and RLL is RLL.
Idk why but the "technical difficulties" with the piano brake down killed me I wasn't expecting something that random upbeat and fast paced in the middle of all the interesting long winded info
I'm not saying I don't like the long winded explanations just that that's what I'm here for. I'm not the best at talking for sure 😂
This could easily have been an 80's video showing off the speed of the newly introduced harddrives! 😄
I love it! Nicely done David!
I thought I was the last person alive that knew MFM and RLL
Unlocks some old memories. When I was about 12 in the 90s I got an old hand me down 286 with basically the same version of DOS 3.3 (Although I think it was the IBM branded PC-DOS)
I had no idea Basic was invented in New Hampshire! As a native, I recognized the historical markers. So cool!
Loved getting a chance to see these in operation in person
Congrats! Your EDS now boots from the C drive, just like a modern PC!
Okay, I did not expect to see a Knight Rider Historian here 😃
Wow! Looks interesting to see BBB as head of some repair tool.
This is awesome! Thanks for the heads up about AJ!
What a fabulous explanation... I've been throwing MFM and RLL around for decades... Now i can throw them around and actually know what I'm talking about.
I love the plastic panel on the front of that drive... a half height cosplaying a full height drive. ;)
I agree as I have never really understood FM, MFM, RLL. Now I do.
Finally someone explains the concept behind mfm vs rll.
I used mfm drives with rll controllers for such a long time with my Amiga 1000 and (Commodore) PCs until IDE showed up.
Why? As kids we recycled broken drives by swapping parts around and used what we got. We basically never had problems with repurposed ST225, ST251 and the full size ones which model number I just forgot, which just worked fine with rll Controllers.
Procom plus has a BBS build into it. It was my first BBS as my dad had procom plus for work. Once I got my BBS going I switched to TriBBS. Back when I had a 8086.. Ah miss those days.
Dumping everything in the root directory makes my hair stand on end XD
The contents of the DOS disks go in C:/DOS, then you put it in your path string
"Idiot with a Hammer" sounds like a good band name.
Very impressive and compelling episode!
Imagine back in 1985 when Amstrad released the CPC 664, an upgrade over the 464 with a 3 inch floppy drive.
Instead of taking 15 minutes for an audio cassette tape to load a game, it would only take a few seconds.
Floppy disks were lightning fast!
As far as I remember, these hdds had a seagate software for low level formatting, and they came with a bad sector continuous paper sheet from factory that you had to type when low level formatting. Because they had bad sectors from factory. Then you could proceed to partition and format. but you had to setup the sector cylinder and head spcts in bios first. Don´t know it was done on a XT. I was a kid and saw my dad doing it infinite times.
@ 19:45 - the clacking noise is usually a system-controlled calibrate action, the pattern depends on the BIOS. Later BIOS firmware on different machines simply trusted the disk calibration data (which the controller could read when it was powered on).
I got one of those MFM emulators recently, prompted by a recent video from Adrian's Digital Basement. Haven't used it yet, but hope to soon!
In the mid 80s, I saved up to buy a hard drive from "Hard Drives International" for an IBM clone PC. ( I couldn't afford a real IBM PC as it was over $2000 back then). It would be my first hard drive, moving up from "floppy boots", and I was pretty excited. The drive I got was RLL, and somehow, I think the RLL drives were less expensive than MFM, which is why I got the RLL (they were expensive back then). Also, that was the first time I heard of RLL, and never forgot what the acronym stood for, but didn't know the tech behind it :)
For some odd reason, I'm subscribed and enjoy your videos. I don't know what you are doing or understand it, but I have a small appreciation of it from my experience with old Apples, Macs, and PCs I used in my youth. Apple II is the oldest Apple computer I used and Win 3.0 is the oldest PC. My justification for watching your videos is that someday civilization might collapse and maybe my brain is frozen or I will be cloned and reawoken in the future and the only way to access these ancient surviving computers is to pull the knowledge of these videos from my brain. I pop one on and just watch it like an old movie or music while drinking my coffee.
p.s. I think the funniest aspect of this is without any clue what's going on, I still pause the video when I go get food or something to drink. It's not like I would notice anything I miss for a few minutes but I hate to hear something interesting happening in the kitchen and have to rewind.
I remember dos 3 all the way through 6.21. Those were the days os ascii, asembly, basic, and 300 baud modems with bbs. When you copied without the sys I knew it wouldn't boot. Some things you never forget like sys and format /s. The coolest thing I ever did with ms-dos 3.2 was change the assembly to say other things. Like RN-BOSS etc. I had the only OS that I customized the message on. It was so easy to edit in the assembly because it was plain text. I could change things like Microsoft to read other words as well. Fun times. Those were the teue hacker days. When the Pink Shirt book came out, every true hacker bought it. That was the ultimate bible for understanding the OS and hard drive storage. If you wanted to write a virus or something that book was gold.
so cute the little bunny
the tech was interesting to but we all know we came here for the animals at the end. ;)
ST238R, my first HDD!
It's been 30 years since I played with RLL drives. I had a 21mb ST225 drive in a 286 running DOS. I do remember it had a clunky, nasty sound when it ran....
Awww that's a cute baby bunny. I want more of that. Time for the channel to make a hard pivot lol
MFM, RLL, Voice Coil termos que ficaram para sempre na memória da gente xD
FDISK... Debug + G=100 + Entrar lista de Bad Sectors + etc :D fiz muito isso nos computadores, naqueles anos. A gente instalava muitos HD, apesar do preço ser alto.
Duas coisas atrapalhavam as controladoras: Mau contato (Mesmo sendo novas) e aterramento. Sim! As fezes, só de colocar um parafuso, mesmo que fechando o gabinete, fazia a controladora ou a placa-mãe ficarem loucas!
Vendo a situação, lembrei de um tempo em que alguns conjuntos (controladora+Winchester) ocorria um problema: Após formatar e transferir o sistema e dar boot, dizia que não havia O.S. para dar boot. Daí, tinha que executar o Sys c: novamente. Com o tempo, descobri o que era (não lembro mais).
Bem, grato pelo vídeo!
That "insane" list of errors was actually common in late 80's when installing Netware. Can't remember the tool but we always had to run a program (sys?) to warn the os of the bad stuff. Then ages of figuring out if track 0 was reliable and then an age of checking the disk. Later versions could handle bad blocks dynamically shaving days of installing a server.
20:14 Yes...cute! It was RIGHT THERE the whole time!
To format the harddrive and transfer system in one step you can use
A>FORMAT C: /S
but also to make your system disk look a little nicer you could place the dos files in a subdirectory by itself.
A>MD C:\DOS
and then copy the diskettes from A -> C:\DOS
A>COPY 'star'.'star' C:\DOS (TH-cam won't show the 'star' character)
to enable the system to find the dos files at the correct subdir you need to add following line to the AUTOEXEC.BAT file
PATH=C:\DOS
Maybe other ppl suggested this too, so I'm sorry if this would be a double entry.
Very nice machine :)
Instead 'star'.'star' you can just type 'dot' eg .
Usually format C: /Q /Y only write an empty File Allocation Table and does not ask for confirmation. This is time saving not to cycle through writing all the cylinders.
@bubullenoiraude you lived in a dangerous fast way! At company level I cannot afford any errors to show up unexpectedly so format without checking for bad sectors was a big NO, No for me and my work.
17:56 I had an ST4096 back in the day.
Looking it up, I see that the difference is that your ST4097 is RLL, as opposed to the original ST4096 which was MFM. Due to this, the higher number of sectors per track gives us the higher transfer rate and capacity.
Thinking way, way back, and with some uncertainty: a handy keyboard thing is the upand down arrow keys. From the command prompt, type UP-arrow and it displays the previous command line. DOS keep a few lines available. Browse through them with UP and DOWN arrows. When you get one you want to repeat, press enter. If you want to edit it, use RIGHT and LEFT arrow keys.
This should work for the Linux OS on the BeagleBone, but does not work for DOS. In DOS you can use the F3 key to bring up the previous command.
You put everything in the root of C:? You monster! 😂
Wait until he get PATH
He's still young and innocent. Forgive him.
Great! I did lots of FDISKs on MFM and RLL drives way back when. About the interleave factor. This is an offset for reading sectors while the HD spins by. If you select the IF properly the drive doesn't have to take another turn. Formating a system drive was basic knowledge in the early 80ies. The boot sector has to be bootable.
Oh, wow, interesting that that converter/adapter has its own built-in drive on it, the SD card one.
I WANT THAT „FORGOTTEN MACHINES“ SHIRT 😤
Blast from the past - thank you. I remember in the mid-80's buying a HUGE 72MB Micropolis drive and then RLL'ing it to 144MB. An yes, my piers thought I was insane for wanting that much storage. I won't admit what I paid for that (used!) 72MB 8" drive But I was successful and became "the man of the hour" Thank you for the infoTainment. The check is in the mai! Cheers from So.Ca.USA 3rd House On the Left.
How are you planning to do file transfer? Write an XMODEM program for the Centurion, and then use Procomm+'s file transfer support (which surely includes XMODEM)? I don't understand why different disk block sizes matter if you are backing up at the file level... Flashback to using KERMIT to transfer files from our VAX/VMS mainframe to my Atari ST in 1987ish...
I was wondering the same thing. The serial transfer would act as an abstraction layer, leaving the program on either end to handle any data storage through the OS. Might need something to make a note of any extra attributes the Centurion's filesystem adds to files or translate them to a DOS equivalent, maybe?
PCPlus does support XModem. ZModem and YModem as well.
FDISK, DEBUG, it all brings back memories from the dark old 80s.
Watching you guys type in linux commands and not hitting tab once was very interesting
Yeah, that's how us linux noobs do it...just bumble through. I think I knew about that tab thing, but I forgot about it in the heat of the moment...
@@ForgottenMachines I was a noob once too, it was just very funny watching you guys work with it. Seeing that drive being read though was very awesome, thanks for helping Usagi dump it.
"Where is the any key, I don't see it on my keyboard." 😁
DOS 3.3 what a new DOS you have there, anyone remember PC-DOS 2.0 and MS-DOS 2.1 ?
Wow. References to sector interleaving. Haven't seen that sort of thing in a very long time. BTW, IIRC, you can type "format c: /s" to format the drive and make it bootable in one step instead of running sys after running format.
MS-DOS format has several options. Re making the drive bootable, /B reserves space on the drive for the system files so that later you can use the SYS command after files have been copied. /S will copy over the required os files for boot after the format has completed. With this option you don't need to use the SYS command afterwards.
The commonly used low-level formats on magnetic storages actually introduce special encodings in the header of the ID and the data block of each sector. This special encoding wouldn't be possible with strict FM or MFM encoding. For instance, see ECMA 125 section 9.12 and 10.2/10.4. The special A1h byte omits a magnetic transition between two bits where it would be necessary for a strict MFM encoding. The controller can (and needs to) detect this byte anyway, which is giving away that it is an RLL detector in reality.
Sys doesn't need it to be freshly formatted. It needs a very specific place in the drive to be empty to place the system files in that specific location. If that specific space isn't free then you get that error regardless of how much free space the rest of the drive has.
if i recall well the rll card was a simple trik to expand the capacity of an old drive. that's the origin of my first 15mb drive
You are so right, I screamed SYS at the screen :D
Is that device basically a Greaseweazle for hard drives? That's really neat!
The interleave factor is a way to tune the I/O speed. IThe optimal for 8-bit buses is 3:1 and 16-bit buses as 1:1. But those are best cases and there are caveats. I mean, if you use an 8-bit card on a 16-bit (eg., 80286) bus, and the optimal interleave is 3 for the card on an 8-bit system, 4:1. So the slower the controller, the higher the interleave you need to get the fastest rate you can get with that configuration. And programs like the older Spinrite and Optune can re-interleave the drive on the fly for you. They can test the interleave factor and reformat to the best. And the 2 programs I mentioned let you reformat in place without necessarily needing to back up your data (though you should).
And yes, a 20 MB MFM drive (17 SpT) would be a 31 MB RLL drive (26 SpT).
31:30 you could have added a /s after the format command to essentially do both steps at once. Been ages since I used that early of a version of DOS, but I know that worked at least with version 5 and later. Should still work on 3.3 though I believe.
Cool video, i'm actual working on an "WANG Professional Computer" (It is an MS-DOS machine witch is not IBM compatible and use ist own card interface no ISA connectors), with some problems with the comunication with the hard drive. It's an MFM Drive, spins up normally and runs through it's self test and the drives service manual says, when the powerlight stays on (What it does) and doesn't blink, the drive is in ready state. After 1 minute of computer selftesting it says "booting from winchester disk..... failed. After that i couldn't test anymore because the damn RIFAS goes up in smoke. But befor i powered it on, i dumped all the ROMs (safety first).