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- เผยแพร่เมื่อ 6 ส.ค. 2024
- In this video from ITFreeTraining, I will look at the Small Computer System Interface or SCSI. SCSI has been around since the 80’s, however it is being replaced by other standards like SAS which I will look at later in the video. Although SCSI is not used in new computers nowadays, it is important to have a basic understanding of it if you are repairing old equipment.
Download the PDF handout: itfreetraining.com/handouts/ap...
SCSI
0:22 SCSI stands for Small Computer System Interface. As the name suggests, it is an interface designed to connect devices to a computer. SCSI has different levels of success in the marketplace and is fundamentally used to connect hard disk drives to computers. However, it could also be used to connect other devices to computers, like optical drives and scanners.
Computers sold on the market today no longer use the SCSI interface. Later in the video, I will look at how SCSI has changed and where you may encounter it today. For the exam, it is good to have an understanding of how SCSI is used today. For the technician, it is good to have a basic understanding, in case you have to fix an old computer that still uses SCSI. To start with, I will have a look at how SCSI works, so you can understand why it was used in the marketplace.
Parallel
1:10 The SCSI interface uses parallel technology. So essentially this means that multiple bits are transferred at once in sync with each other. You may be thinking that there were a lot of other interfaces that also transferred data in parallel, so what made SCSI different?
SCSI generally transferred data faster than its competitors. Although there are many different versions of SCSI which have different speeds, let’s consider an example of what sorts of speeds we are looking at, compared with a competitor.
Back in the 90’s, SCSI was transferring data at 320 Mega Bits per second whereas IDE was transferring at 133 Mega Bits per second. There were different versions of each which ran at different speeds, however this will give you an idea what speeds were available at the time. The main take away is that SCSI ran faster than the competing products. This extra speed cost more money to implement, and thus SCSI devices cost more than their competitors.
Due to the higher cost, SCSI devices tended to be used on high-end workstations and servers. Some manufacturers like Apple used them for a while. Essentially, in the old days, if you wanted more performance you would get SCSI; however, you would pay more for it.
SCSI Connectors
2:26 There were many different versions of SCSI over the years. Each version of SCSI offered increased speed, and with the different versions came many different connectors. You can see some of the connectors that SCSI uses. There are too many to go through and there is not much point learning them since SCSI is not used in new computers any more. If you are fixing a computer and see a connector like one of those shown, you are probably working with SCSI.
It is unlikely that you will get tested on the old SCSI technology in the exam, but I will go through some basic things so you will have an idea how to support it if you come across it.
Description to long for TH-cam. Please see the following link for the rest of the description. itfreetraining.com/ap/1c45
References
“The Official CompTIA A+ Core Study Guide (Exam 220-1001)” Chapter 3 Position 11012-11292
“CompTIA A+ Certification exam guide. Tenth edition” Page 303
“Picture: External SCSI Connectors” www.scsi4me.com/scsi-connector...
“Picture: Picture of rear of SCSI device” en.wikipedia.org/wiki/File:Sc...
“Picture: SCSI terminator ” commons.wikimedia.org/wiki/Fi...
“SCSI (Small Computer System Interface)” www.linktionary.com/s/scsi.html
“Picture: SAS Connector” commons.wikimedia.org/wiki/Fi...
Credits
Trainer: Austin Mason ITFreeTraining.com
Voice Talent: HP Lewis hplewis.com
Quality Assurance: Brett Batson www.pbb-proofreading.uk
Your channel name encompasses perfectly what you do. Instant subscribe.
Glad you like the videos and thanks for the sub.
Thank you fella you really helped me out in understanding
Glad it helped
In the past i had to use iscsi to trick a programm on my computer to think that the raid partition on my NAS would be an internal harddrive. Worked great and i could even play games over it
Sounds good. People still use iSCSI to do that. It is a cheaper option than using fibre channel.
Thanks. Great vid and clear explanation.
Glad you enjoyed it!
Thanks for this amazing Video.
Thank you
Scsi is scaring me in my studies, i just need on hand training to understand it more.
It is difficult now days to learn since the technology obsolete.
dude you are great
I appreciate that!
you should add a pic of a sata hdd and a sas hdd, this shows that a SAS HDD can not be attached to a sata interface however a sata hdd can be attached to a sas wire even many sas controllers
This was great. Do you have a video like this for PATA/IDE?
Glad you liked the video. Here is a video on IDE/PATA
th-cam.com/video/CF_copQaORQ/w-d-xo.html
Thank you
You're welcome
Wow, Fantastic. What do you think in this videos, everyone?
I think: Is SAS only bidirectional over the two physical connections to a drive or also on one connection?
SAS support topologies. So you can connect multiple SAS device together. kind of like networking for storage.
i have an energy meter, uses floppy with scsi 26 pins, i don't know how can i adapt that to an emulator floppy, to use an sd or usb flash,
I am not sure it is possible.
This article talks about a SCSI to USB connection.
www.tech-faq.com/how-to-connect-scsi-to-usb.html
Maybe is you could connected the energy meter to a computer and have a computer emulator a floppy drive that may work. Not sure how you would go about doing it.
Thanks
Thanks very much.
Man, no dissuasion of high voltage scsi? I had a 3590 that was a pain to get working because of the card type needed.
We have a newer version of the video which look at this topic in more detail.
th-cam.com/video/jmiZ0gEBEk4/w-d-xo.html
Hi sir
Please upload videos for cloud.
We are working on A+ course at present. Will consider cloud videos later on.
can you daisy chain a scsi jaz 1G off of a zip 100?
I would say you would be able to, assuming they use the same type of SCSI. A lot of external devices back than used SCSI SE, so the bus should reduce down to the slowest device on the chain. Can't say for sure it would work, but good chance it will. Just make sure that you give them different SCSI ID's.
Anyway to recover the data off of these hard disks?
Depending on what the problem is, there are options available. Given the age of the technology now would make it difficult to get parts and equipment.
I know your just providing just a general overview, but last time I had anything to do with legacy SCSI the controller also had a SCSI ID. A Comment on that might be in order.
That is mention at 5:00 in to the video. It talks about the switches or counter on the back of the device to set the SCSI ID.
@@itfreetraining talking about the controller itself. Most people wouldn’t consider the controller to be a device in the chain
@@norlag I see what you are saying now. Yes, we did forget to mention that.
@@itfreetraining yes on my Adaptec 29160N PCI Ultra160 SCSI card it designates ID-7 for the SCSI controller.
I generally asking me from where the "A" came into the pronouncing ? Small Computer System Interface...... SC "A" SI ? ;)
It’s just how it’s pronounced, impossible to pronounce a word without vowels
It's actually pronounced "scuzzy".
You got your bits and bytes mixed up in your definition of SCSI and IDE speeds. Both should have been in megabytes per second not megabits per second.
cable managment was a mess ;D
SCSI could get messy when you had a lot of devices daisy chained together.
Really nice 👌 😍💋 💝💖❤️
Thank you! Cheers!
I've been using SAS for years now already and what he talks here is mostly gibberish, theoretical but not real-world, in real world only 1x to 4 device sas is possible at most (and is usually the standard, oddity when less that 4 headers are coming from "minisas")
You are aware that SAS is often used for large storage like SANs and cloud storage? These have a lot more SAS drives than that. I worked on a server recently that has 20 SAS drives connected via RAID to local storage. I am guessing you only have work on individual drives.
@@itfreetraining it's been 7 months and I don't remember what I commented about, but MiniSAS is up to 4x, those servers have many mini-SAS ports, not 1
My servers have only built in 1 or 2 minisas headers but adapters and what's it called - the middleplate have many ports
Thank you fella you really helped me out in understanding
Glad it helped