TU58 - I had 2 of those in my home VAX11/730 little cassettes block based which was interesting. VAX11/730 had its microcode on tape usually the least accessible tape drive and took 20 odd minutes to load it to the VAX chevron >>> unless you auto booted then it came up on the massive RA80 (120MB from memory) and also had an RL02 - 10MB removable single platter disk pack - I miss my VAX11s had a 11/730 and then upgraded to a VAX11/750 (booted from rom and instruction set built in) joys of hacking away while warming up the house! VAX 11/750 also had a TU58 for a while was trying to access it straight via MACRO-11 the controller was packet based you sent a series of bytes to it with a checksum and would do whatever was in the command packet. I have a VAX8300 as my dev machine running macro assembler and then fed console commands to the 730 to update the code - took forever to get the tape drive to a simple thing - much easier with the VMS TU58 tape driver :)
This was great, first time I've seen one of these. We used to carry a TU-58 twin dectape cartridge drive around for loading diagnostics onto faulty machines, and a DL11-W for those machines that didn't have a serial port, which not all of the control machines did, then key the loader in by hand. How times have changed !!
Thank you! brings back lots of memories servicing and operating these machines in the late 70's into the 80's. They mostly ran like tanks, and were relatively easy to diagnose and repair.
Holy smokes...I used to have to align a TU-78 tape drive connected to a VAX 11/751 back in my USAF days...it had dual air columns so that it didn't stretch the tapes....this is bringing back so distant memories!! Great video...thank you!
I have seen those tape drives in many PDP pictures, but never used/running. I always assumed they were paper tape drives as all the magnetic tape drives I've ever seen use way bigger tape reels. The little reels remind me so much of paper tape from teletypes etc.
13:46 “SJ” = “Single Job” (i.e. single process). There was also an “FB” (“Foreground/Background”) version of RT-11, which could run a separate background process while the foreground one interacted with the user in the normal way.
Thanks or the interesting video. I have 5 pdp computers, but they have no TU56s. I've always wanted a DECtape, but had no idea that there was so much control electronics associated with them! You've done a huge amount of work getting that all working. Congratulations! Btw: It would be nice to have seen a front-on view of the drives operating, so that we could see what the lights indicated.
11:30 These drives were invented at MIT Lincoln Labs as part of their “LINC” computer project. This design was then passed over to DEC, who made some “LINC-8” machines, which were combination of LINC and PDP-8. The mini tape drives (renamed “DECtape”) were so handy, they outlived the original LINC concept, and continued to be used I think into the VAX era.
AIUI, they were original called LINCtape, though I don't think that the LINC and DEC formats are quite interchangeable -- I might be wrong on that; I was always at the other end of a dataphone from the box. 🙂
The tape heads were not truly redundant. There were three pairs, each pair had their coils in series. Hopefully if one head was over a bad spot of tape, the other one would be on a good spot, so the data would survive, if at half-amplitude. The PDP-8 operating system asked each progfram to supply a few hint bits in order to minimize unnecessary dectape motion. One bit said that the program didn't bash the keyboard monitor, so then the OS wouldn't save and restore that area. Another bit indicated that the program didn't bash the USR area, where all the OS's functions were. I never bothered to specify those hint bits as we always had a RK8-E disk drive which did those save/restore operations in a blink of an eye. Would have bothered if we had to work with DECTape.
I was servicing the Artronix Pc-12 that uses the same tape unit and I think tha same encoding. also I repair PPD's but they use HD's the firs 8" Winchester units. Old times!
Amazing how overbuilt those drives were. Need to wrap a tape around a spindle? Let's give it enough torque to move a car. :D Also wirewrapped boards scare me so much. Can you imagine the cursing if you have to undo a wire at the bottom of the whole ratnest?
Wonder if you still have the original basic games from the 70s? We used one of these with a PDP11/15 in the late 70s, it was such a relief to give up the hazards of managing large multi-tape programs. 😂 I had a fault on one of the dual slot cards once, just changed the faulty bus driver chip. Did you know they had an automated computer controlled unit to wire their backplanes? If you had the multilayer boards, later than these I think, it was important to check all the connections to each pin and add mylar wire as necessary/extra solder. The DEC Field Service engineer used to exchange them with ones repaired in Holland. When the field service stopped we got a contract direct with Holland. I’m thinking somebody still has lots of LSI11/23 cards.
It shows the effect of Moore's Law well I think. The two CPU modules contain about 200 SSI/MSI TTL circuits with on average 50 transistors each, totalling maybe 10000 transistors. A Pi zero maybe have 500 million transistors?
No. I don’t have this image dumped. It is fairly easy to creat a bootable RT-11 image inside SimH using any of the available RT-11 distributions which are online. The set of four RX01 images I have put at www.datormuseum.se/documentation-software/rx01-and-rx02-floppy-disks should be useable in this case.
The format is more elaborate. The track is divided into lines clocked with a clock signal in the clock track. Each line has three data bits and one mark bit. Six lines are combined into a 18 bit data word and a 6 bit mark word. The mark word tell what type of data is in the data word. Might be a check sum, a block number or actual user data. For a PDP-11 the two highest bits go unused and only the lower 16 gets transferred (normally) to the computer.
I am curious if a machine like this can record music like a reel to reel. I know it's data. These machines are before my time. Could you copy an MP3 song to a device this and read it back if the file size is under 300KB?
In theory you could record a 300 k song on the tape. But I don't think that it will be able to decode the MP3 format i real time. Remember that the speed of a PDP-11 is at most 1 MIPS. The 11/05 is probably around 0.5 MIPS. The transfer speed from DECtape is rather low as well. Approximately 200 us per 16 bit word as far as I remember.
@@mattislind4443Mp3 at low bitrate. I was curious because it looked like you were using a modern pc to access the data. Maybe not stream it off the tape but copy it then play.
@@coondogtheman Low bit rate, yes, perhaps. I know very little about how MP3 decoding is done. Then the question is if you can fit the decoder in 56 kbyte of memory? Perhaps possible with a good deal of assembly programming. Aside from that you need to add a D/A converter board. I think that other type of music generation should be possible, though. Either by algorithms or stored waveforms, perhaps? The modern PC is only used as a terminal connected over a serial port to the PDP-11 and is just used for interacting with the operating system running on it.
@@mattislind4443 I dont mean run the mp3 player program off the tape or the small amount of memory. Can you access this tape drive on a modern PC? If so you could just use the tape to store the song and not the mp3 player program.
TU58 - I had 2 of those in my home VAX11/730 little cassettes block based which was interesting. VAX11/730 had its microcode on tape usually the least accessible tape drive and took 20 odd minutes to load it to the VAX chevron >>> unless you auto booted then it came up on the massive RA80 (120MB from memory) and also had an RL02 - 10MB removable single platter disk pack - I miss my VAX11s had a 11/730 and then upgraded to a VAX11/750 (booted from rom and instruction set built in) joys of hacking away while warming up the house! VAX 11/750 also had a TU58 for a while was trying to access it straight via MACRO-11 the controller was packet based you sent a series of bytes to it with a checksum and would do whatever was in the command packet. I have a VAX8300 as my dev machine running macro assembler and then fed console commands to the 730 to update the code - took forever to get the tape drive to a simple thing - much easier with the VMS TU58 tape driver :)
Amazingly complicated in the old days! Wow. The closest I had was the PET2001 with a cassette drive built-in. Amazing how far we have come!
This was great, first time I've seen one of these. We used to carry a TU-58 twin dectape cartridge drive around for loading diagnostics onto faulty machines, and a DL11-W for those machines that didn't have a serial port, which not all of the control machines did, then key the loader in by hand. How times have changed !!
Thank you! brings back lots of memories servicing and operating these machines in the late 70's into the 80's. They mostly ran like tanks, and were relatively easy to diagnose and repair.
At high school in 1976 we had a PDP 11/10 running CAPS-11 and a dual cassette drive which was VERY impressive in it's operation! :)
Holy smokes...I used to have to align a TU-78 tape drive connected to a VAX 11/751 back in my USAF days...it had dual air columns so that it didn't stretch the tapes....this is bringing back so distant memories!! Great video...thank you!
I have seen those tape drives in many PDP pictures, but never used/running. I always assumed they were paper tape drives as all the magnetic tape drives I've ever seen use way bigger tape reels.
The little reels remind me so much of paper tape from teletypes etc.
13:46 “SJ” = “Single Job” (i.e. single process). There was also an “FB” (“Foreground/Background”) version of RT-11, which could run a separate background process while the foreground one interacted with the user in the normal way.
Thanks or the interesting video. I have 5 pdp computers, but they have no TU56s.
I've always wanted a DECtape, but had no idea that there was so much control electronics associated with them!
You've done a huge amount of work getting that all working. Congratulations!
Btw: It would be nice to have seen a front-on view of the drives operating, so that we could see what the lights indicated.
11:30 These drives were invented at MIT Lincoln Labs as part of their “LINC” computer project. This design was then passed over to DEC, who made some “LINC-8” machines, which were combination of LINC and PDP-8. The mini tape drives (renamed “DECtape”) were so handy, they outlived the original LINC concept, and continued to be used I think into the VAX era.
AIUI, they were original called LINCtape, though I don't think that the LINC and DEC formats are quite interchangeable -- I might be wrong on that; I was always at the other end of a dataphone from the box. 🙂
The tape heads were not truly redundant. There were three pairs, each pair had their coils in series. Hopefully if one head was over a bad spot of tape, the other one would be on a good spot, so the data would survive, if at half-amplitude.
The PDP-8 operating system asked each progfram to supply a few hint bits in order to minimize unnecessary dectape motion. One bit said that the program didn't bash the keyboard monitor, so then the OS wouldn't save and restore that area. Another bit indicated that the program didn't bash the USR area, where all the OS's functions were.
I never bothered to specify those hint bits as we always had a RK8-E disk drive which did those save/restore operations in a blink of an eye. Would have bothered if we had to work with DECTape.
I was servicing the Artronix Pc-12 that uses the same tape unit and I think tha same encoding. also I repair PPD's but they use HD's the firs 8" Winchester units. Old times!
That tape looks as thick as parcel-tape 🙂
5:18 Those 104xxx instructions are EMT instructions. Presumably they are system calls into the diagnostic monitor (XXDP, was it called?).
Amazing how overbuilt those drives were. Need to wrap a tape around a spindle? Let's give it enough torque to move a car. :D Also wirewrapped boards scare me so much. Can you imagine the cursing if you have to undo a wire at the bottom of the whole ratnest?
Wonder if you still have the original basic games from the 70s?
We used one of these with a PDP11/15 in the late 70s, it was such a relief to give up the hazards of managing large multi-tape programs. 😂 I had a fault on one of the dual slot cards once, just changed the faulty bus driver chip. Did you know they had an automated computer controlled unit to wire their backplanes? If you had the multilayer boards, later than these I think, it was important to check all the connections to each pin and add mylar wire as necessary/extra solder. The DEC Field Service engineer used to exchange them with ones repaired in Holland. When the field service stopped we got a contract direct with Holland. I’m thinking somebody still has lots of LSI11/23 cards.
The original games came from field service, they were all .BAS
Yeaps, I used to boot program our PDP11s from my own memory every morning before I made coffee for the shop (!Coast Guard Rules! ;).
Amazing how even a pi zero will smoke it in every aspect, yet this cost more than a house when it was new.
It shows the effect of Moore's Law well I think. The two CPU modules contain about 200 SSI/MSI TTL circuits with on average 50 transistors each, totalling maybe 10000 transistors. A Pi zero maybe have 500 million transistors?
And will probably cost as much as a house in a few years time. Sadly, there are fewer and fewer of these amazing machines each year.
Except you can't use the pi zero to heat your office. ;-)
Interesting video, thanks
Great video Mattis, love it.
I really should get my DECtape operational ...
Where did you find the replacement motor run capacitors?
Thanks Henk! 100uF 100VDC ordinary polyester film capacitors from Mouser: www.mouser.se/Search/ProductDetail.aspx?R=R60EW61005000K
There are also "motor start/run" capacitors which are a bit cheaper and come with quick connect terminals.
there are function codes for 1 2 & 6.
are there also ones for 3 4 and 5 ?
if so, what are those for ?
13:22 seems like the controller cannot run both drives at once. Or is that a limitation of the OS?
10:35 Would it run with drive 0 write-protected? Battle-scarred sysadmin speaking here ...
Good grief. I only used RT-11 with a hard disk. It seemed to boot instantly.
Very nice video. Is an image of the bootable tape you used available somewhere, so that could use it with SimH (on the PiDP-11)?
No. I don’t have this image dumped. It is fairly easy to creat a bootable RT-11 image inside SimH using any of the available RT-11 distributions which are online. The set of four RX01 images I have put at www.datormuseum.se/documentation-software/rx01-and-rx02-floppy-disks should be useable in this case.
15:30 Is “BLKJAK” a “Blackjack” game?
very nice video :)
Thank you very much for appreciating it!
It's nice to see old hardware is restored and brought back to life :)
So 3 data tracks would mean 2^3 bits of data. 8 bits. So run the data through a 74(LS/S/AC)138 3 to 8 decoder and have your 8 bit characters.
The format is more elaborate. The track is divided into lines clocked with a clock signal in the clock track. Each line has three data bits and one mark bit. Six lines are combined into a 18 bit data word and a 6 bit mark word. The mark word tell what type of data is in the data word. Might be a check sum, a block number or actual user data. For a PDP-11 the two highest bits go unused and only the lower 16 gets transferred (normally) to the computer.
I am curious if a machine like this can record music like a reel to reel. I know it's data. These machines are before my time.
Could you copy an MP3 song to a device this and read it back if the file size is under 300KB?
In theory you could record a 300 k song on the tape. But I don't think that it will be able to decode the MP3 format i real time. Remember that the speed of a PDP-11 is at most 1 MIPS. The 11/05 is probably around 0.5 MIPS. The transfer speed from DECtape is rather low as well. Approximately 200 us per 16 bit word as far as I remember.
@@mattislind4443Mp3 at low bitrate. I was curious because it looked like you were using a modern pc to access the data. Maybe not stream it off the tape but copy it then play.
@@coondogtheman Low bit rate, yes, perhaps. I know very little about how MP3 decoding is done. Then the question is if you can fit the decoder in 56 kbyte of memory? Perhaps possible with a good deal of assembly programming. Aside from that you need to add a D/A converter board. I think that other type of music generation should be possible, though. Either by algorithms or stored waveforms, perhaps? The modern PC is only used as a terminal connected over a serial port to the PDP-11 and is just used for interacting with the operating system running on it.
@@mattislind4443 I dont mean run the mp3 player program off the tape or the small amount of memory. Can you access this tape drive on a modern PC? If so you could just use the tape to store the song and not the mp3 player program.
Nice vidieo of reading a tape.