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From: Torbjorn Lindgren <tl@none.invalid>
Newsgroups: comp.arch
Subject: Re: Is Parallel Programming Hard, And, If So, What Can You Do About
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Date: Thu, 22 May 2025 12:12:52 -0000 (UTC)
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BGB  <cr88192@gmail.com> wrote:
>I also remember from some early 90s PCs some CD-ROM drives that used 
>some sort of non-standard interface. Typically, they would plug into an 
>ISA card with a cable that was (IIRC) somewhat narrower than a normal 
>IDE cable (I remember it being around the width of a floppy cable; two 
>ends with a direct connection, and no twists, unlike a typical floppy 
>cable which usually has part of the cable twisted).
>
>Not entirely sure what it was. Wasn't an IDE/ATAPI CD-ROM though, do 
>know this much at least...
>
>Digging more, there was apparently a proprietary 34-pin Sony connector, 
>which does at least resemble what I remember (and some of the drives do 
>look like the drives I remember seeing).

The common pre-ATAPI CD-ROM interfaces were SCSI, Panasonic/MKE,
Mitsumi and Sony, early on there was also LSMI/Philips but they
switched to one of the other fairly early. Which of these were most
common isn't easy to tell any longer.

There were cheap dedicated interface cards for all of these but most
people bought them bundled with soundcards which included the correct
interface on it. These cards (both dedicated and on soundcard) were
often PIO-only (instead of DMA) which was fine for a 1/2/4x CD-ROM but
not much else.

Later soundcards often had all three "main" interfaces to reduce the
number of SKUs they need and make it easier for customers, later
soundcards switched to providing a (usually gimped) ATA interface -
which then was removed a few years later as ATA interface was
everywhere already.

Panasonic & Mitsumi uses unkeyed 40-pin cables (unkeyed IDE cables can
be used) while Sony went with the 34-pin floppy cable. In all cases
they were not compatible with actual IDE/ATAPA or floppy cards despite
the cable fitting... Yes, there were multiple incompatible non-IDE/ATA
CD-ROM with 40-pin connectors because OF COURSE...

The soundcard ATAPI headers that replaced them were often usable with
disks with the right drivers but performance was usually not very
good.


>*: Had once encountered a computer (that at the time was being 
>discarded, but I got it and had it for a while). It had SCSI drives, and 
>also the weirdness that rather than the CPU and RAM being on the 
>motherboard, it was on a riser card (the MOBO was IIRC effectively just 
>card slots, IIRC they resembled 16-bit ISA slots buts with a long 
>extended part on the front; similar to the "VESA Local Bus" IIRC).
>
>IIRC, no connectors on the MOBO (apart from power IIRC), all of the 
>external connections (like VGA and mouse/keyboard) being on riser cards.
>
>I remember the CPU riser card apparently having dual 486DX's, but from 
>what information I can gather, multi-socket systems weren't a thing with 
>the 486, so don't know what was going on there. Beyond this, was SIMM 
>RAM, and a lot of other stuff you would normally see on the MOBO 
>(excluding connectors).

Could be a Compaq SystemPro[1]? Not sure if there was any other 486
multi-CPU machines that were DOS/Windows (single-CPU) and Windows NT
compatible (IE ruling out Sequent Symmetry).

The daughtercard method isn't restricted to these, IBM used it a lot
on their high-end PS/2 and I've seen it used by someone on pretty much
every generation after, back in the days it wasn't uncommon to run out
of space on the main motherboard. 


>It was a weird machine, I had managed to get Win NT4 installed on it, 
>but I remember I couldn't do much else with it at the time. Also for 
>some unknown reason, while normal 16-bit ISA cards would plug into the 
>slots, they did not seem to be recognized by the OS.

If it was an original SystemPro they appear to be A-SMP (due to being
designed around the '386) so not everything can run on the "second"
CPU, perhaps that what you remember?

The SystemPro XL appears to be Compaq's first full ("real") SMP 486
machine, this too appears to have leaned into using daughtercards.
This should behave more like a "normal" multi-socket machine.

Both may well be "first" - Compaq was really leading the field at this
point.

1. https://en.wikipedia.org/wiki/Compaq_SystemPro