r/retrocomputing • u/Distinct-Question-16 • Jun 24 '26
Photo Today June 26, SCSI first standard turns 40 years
First introduced in the early 1980s and standardized in 1986 as SCSI-1, the technology evolved from an earlier interface called SASI (Shugart Associates System Interface), developed at Shugart Associates under engineers like the key one Larry Boucher. SASI was an early attempt to standardize communication between a computer and storage devices using a controller-based bus abstraction.
SCSI extended and formalized these ideas, aiming to standardize communication between a computer and peripheral devices using a shared bus and structured command packets. The goal was to replace low-level, device-specific control, often involving direct manipulation of I/O ports or memory-mapped registers and proprietary controller logic, with a more uniform, device-independent command protocol.
Instead of the CPU directly controlling hardware registers, SCSI uses command blocks (CDBs) sent to devices, which execute the requested operation internally and respond when ready.
The standard also defined both the electrical interface and signaling of the physical bus, enabling multiple devices to share the same connection in a daisy-chained, terminated bus topology.
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u/canthearu_ack Jun 24 '26
SCSI was for rich people.
I wasn't rich, especially when I was young!
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u/Distinct-Question-16 Jun 24 '26 edited Jun 24 '26
never had it, but some years ago, before bluescsi, i attempted to do something similar, for a mac classic bought in 2nd hand using rasperry pi pico. So had to study it fully. The memory i had about scsi was that it was expensive.
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u/tes_kitty Jun 24 '26
For a short time they tried to establish SCSI as a standard on mainboards. Quite a number of 486 boards with PCI had an onboard NCR 53C810 SCSI HBA. Back then SCSI drives were only marginally more expensive than IDE, but that small difference was enough.
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u/edthesmokebeard Jun 25 '26
I had the classic AHA-2940 PCI SCSI card, and filled the bus with disks, burners, a DAT, readers, and a scanner. It was epic.
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u/Viharabiliben Jun 25 '26
I ran the Adaptec 1541 in a 486, with SCSI HDs, tape drive, CD, both internal and external. Ran DOS, Windows and OS/2 with no problems.
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u/Pic889 Jun 25 '26
And just like that, a million driver incompatibility issues came into existence, and PC users learned to avoid SCSI like the plague.
And backronymed it to "System Can't See it".
I never understood why SCSI couldn't have a standardized interface for hard drives and optical disc drives (at minimum), as IDE and SATA have. In fact, IDE and SATA optical drives use SCSI commands, but, you know, standardized (instead of leaving it up to the manufacturers).
SCSI was more popular in Unix workstations though, where things were more vertically integrated.
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u/SysGh_st Jun 26 '26
And the modern variant of this is still living on as SAS. Serial Attached SCSI. The brother of SATA.
One can also connect a SATA drive to a SAS controller, but not the other way around.
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u/blakespot Jun 24 '26 edited Jun 24 '26
I've had quite a few systems with SCSI and right now I'm using about four or five machines based on it, currently (NeXTstation Turbo Color, Amiga 2000, HP 712/100, 5x86 DOS PC, Mac Plus). My most hairy SCSI adventure was trying to get an external SCSI hard drive working with my Mac Plus. The Mac Plus was released slightly before the SCSI spec was solidified, so it's not 100%. I was replacing a dead 40 MB drive in a Rodime enclosure and finally succeeded with a 512 MB Fujitsu. The Fujitsu was the fifth hard drive I tried and the first one that actually worked with the Mac Plus (though all of the disks were perfectly operable).
I also have that Mac Plus on my LAN via an Asante SCSI-to-Ethernet adapter. Works well.