SCSI, usb of the 80s

In the 80s there was no USB, yet there was a wildly used technology that let us connect hard disks, cdrom drives, scanners and printers even Ethernet interfaces and that was SCSI.

00:00 - Introduction
00:16 - Brief word from our sponsor
00:41 - Why make SCSI in the first place
02:35 - Things get sassy
03:30 - Scsi becomes the standard
05:49 - The BUS
09:16 - Some of the computers that used scsi
09:40 - IDE the rival
14:11 - Servers and RAID
15:20 - Tape drives
17:13 - CD-ROM
19:30 - Multi host
21:43 - The evolution of the standard
25:53 - Adaptec
27:14 - USB
30:00 - SAS
31:20 - Fibre channel
33:17 - Thank you for watching

[vwestlife]

Atari's Serial I/O (SIO) bus was the USB of the '80s. It is credited as the basis of USB, allowing multiple peripherals to be accessed via a plug-and-play serial bus.

[shadesofbeige]

I named my dog SCSI. It's always fun to watch the increasingly distant stares of strangers as I explain how to pronounce "SCSI" and what it means.

[bluefirexde]

That was a lot of mindblows. From the origin of tar over where /dev/sda came from to the fact, that USB Mass Storage uses SCSI commands 🤯

[mikeselectricstuff]

Excellent detailed overview. One minor additional detail - for multi-initiator systems, the SCSI ID was used to indicate which device should be prioritised during the arbitration phase of a SCSI transaction. That's why there are only 8 IDs on an 8-bit bus - each device asserted the bit corresponding to its ID, allowing multiple devices to be uniquely detected.

[CommieGIR]

I grew up with SCSI as I worked on Mainframes out of High School. SCSI was amazing compared to ATA, being able to have 16+ devices on a single chain was always amazing.

It still gives me a little bit of glee working with SAS devices and saying the name Serial Attached SCSI out loud. SCSI still lives with us.

[videodistro]

Here's the one that will surprise you. The Yamaha PMD1 console used SCSI to interface their DSP angine, console and audio interfaces to each other. The longest SCSI cables were 100 meters long, to connect from.stage to other devices at front of house. There you go. I had learned about SCSI with my Amigas so was surprised to see SCSI with the consoles.

[gxfif]

In my first job, I designed SCSI peripherals (mainly tape streamers though blocked tape devices too) at a small British company. I then went on to become a Field Applications Engineer for SCSI devices looking after the Symbios Logic (ex NCR) range of chips and RAID controllers. I still smile when I see how USB, SATA and other interfaces have taken the SCSI command set and use that in their interfaces.

The box at 6:30 looks very much like one of the ones we used for our products, including a parallel port to SCSI tape interface.

There are some interesting points about SCSI which you didn't pick up in the video. Initiators were often left at ID7 because that was the highest priority ID (7 -> 0 then 15 -> 8). Better than that, when you mixed wide (16 bit) and narrow (8 bit) devices on the same bus, they could all still talk because they could all see ID7 and then would negotiate the width of communication. This made it great for customers who didn't have to go out and buy all new kit when they changed bus sizes.

Also, related to the DMA aspect, is that once the initiator selected the target, it was the target that ran the show by choosing what was going to happen and when. Your computer would say "I want blocks 100-105" but the hard drive would be responsible for fetching the data, and then calling back the computer, for the transfer. Assuming that the computer was boss was an all-too-common fault in software driver design for SCSI devices, though it did get me a few all-expenses paid trips to nice locations fixing the problems 🙂

[spikeevans]

Another feature that SCSI had before IDE/SATA was command queing. This allowed the drive to optimize access to the disk. A big feature of SAS was the expanders, which allowed networks of drives to be attached (somewhat similar to FC). Your video was very interesting to me as I worked as a firmware engineer for enterprise disk drives and saw the transitions from SCSI-1 to SAS.

[mattelder]

7:33 There actually is somewhat of a "standard" internal USB connection. It's the header on the motherboard that front panel USB is connected to. There are actually two, one for USB 2, and a different one for USB 3.

[jasonhaman]

Having worked a bit with SCSI for about 25 years, I expected this to be just a nice nostalgic trip down memory lane (which it is). But I was completely unaware of Ultra640. And SCSI printers. And I learned of Adaptec's fate literally yesterday, while researching RAID options for a budget build-your-own server. Fantastic video, thanks! (Oh yeah, had a nice chuckle at the fudge.) I would only add that from about the mid-to-late 90s on, SCSI hard drives themselves were higher-performance than EIDE, separate from the interface. Just because SCSI drives were already chosen for performance, they had 7200 RPM spindle speeds when EIDE had 5400; then SCSI had 10, 000 RPM and EIDE/SATA 7200, then 15, 000 RPM for higher-performance SCSI (or was 15k after SAS took over?) SCSI hard drives also had 5-year warranties, compared to 3-year for IDE.

[kFY]

IDE (or, more accurately, ATA) originally wasn't anything remotely like a competitor to SCSI. ATA literally means "AT Attachment", with AT referring to the IBM PC/AT of course. In its original incarnation it was little more than just a way to plug hard drives into the ISA bus almost directly. A far cry from SCSI which was intended as a cross-platform standard from the beginning - so they were very different beasts, even putting performance aside. ATA only became cross-platform many years later, around the mid-90s.

[jammin]

I love your enthusiastic narration. I had a lot of dealings with SCSI back in the day. It was a running joke in the sysadmin community that, as well as selecting the right ID and ensuring the correct termination, you also had to perform the correct ritual sacrifice of chickens/goats/etc to appease the SCSI gods and get your devices to work properly. In my first job looking after unix workstations I had to deal with about 5 different versions of the standard all in use concurrently. Most of them could be made to talk to each other but if LVD was involved all bets were off (maybe we just didn't have the right adapter...)
One small correction: it's SyQuest (pronounced like the psy in psychology) not SysQuest.

[kse]

We had a SCSI laser printer on our Mac IIcx when I was growing up. Printing was the only thing besides a hard lockup that could stop the cursor moving; normally cursor movement is such a high priority on old Macs it would always work smoothly no matter how busy the CPU was.

[BlackEpyon]

I was wondering why Adaptec cards were so robust. They invented the damn thing!

[awetisimgaming]

I've been using my home server nas thing with a sas hba as well as a striped pair of nvme because of zfs. I'm quite impressed that all of this technology is able to talk to ancient crap still, like a floppy drive I have in the same server. This is mainly because it's also my ingest machine for literally any generation of tech, and I have retro and new machines hooked up simultaneously. I'm glad this work was done so I can play with stuff that has no right being together.

[neil]

Another feature of SCSI was Native Command Queueing which greatly improved performance by allowing out of sequence I/O. SATA drives can now do that as well. SCSI drives also had higher spin speed that IDE - not because of the technology, but because they were higher priced enterprise drives and those drives were usually SCSI. While PC users thought 7200rpm was fast, at work we only dealt with 10k and 15k drives.

[richardcarlson]

As a Mac user from 1985 I got real good at building SCSI chains, sometimes one needed to get pretty creative; between devices with 2 DB or Centronic connectors (or occasionally one of each), the odd device with only one connector, and varying ways to set the SCSI ID and whether the chain needed to be terminated made for an interesting time. I had so many cables, with either type of connector or one of each again, it got pretty confusing unless you understood the craziness.

[SparkRattle]

I remember having a HP Scanner and Printer combo connected with SCSI as part of my first computer set. Really brings back memories.

[borgdylan]

I remember my Computer Studies teacher teaching us about SCSI. At the time I was still 14 years old and had IDE disks and ATAPI equipped optical drives in my computer. Later on I got SATA based machines. I suspect that all these still use the SCSI command set since the linux kernel implements most IO as part of the scsi driver coupled with ata drivers (for ide/sata)

[koenlefever]

USB was inspired a lot by Atari's SIO (Serial Input/Output) from 1978.

The video also reminds me of HP-IB (Hewlett-Packard Interface Bus), a late 1960's parallel bus allowing daisy-chaining, later standardized as the IEEE-488 GPIB (General Purpose Interface Bus). It was used for floppy and hard disks (e.g. by the Commodore PET and the HP-85), but mostly for lab equipment (oscilloscopes, logic analyzers, programmable power sources, digital multimeters...)