8-bit IDE

From: Richard Erlacher <edick_at_idcomm.com>
Date: Tue Apr 18 16:16:37 2000

You're correct all right, Eric, but I'm not interested in making ANY IDE
drive work. I'm interested in the ones too small to bring even $10 at the
flea market, i.e. the ones that are 10x what I need but only cost $6 or so.
I'm not headed for production, and I'm not getting paid, so I want it to be
simple to build. I can hunt a little for the appropriately optioned drives,
if they exist in the form factor I need.

It takes more than a latch, by the way, since you have to latch and hold the
low byte on writes, and the high byte on reads, in order not to screw up the
order of the bytes. Consequently, you need not only the two latches, but a
bit of logic to effect the byte steering on reads and to perform the write
after the CPU does the write, since the only time you can guarantee data
valid is at the very end of the write strobe.

The reason I'm whoring after the few drives with this feature included is
that when this feature was available, if at all, the popular drives were of
about the "right" capacity for the typical application of CP/M.

----- Original Message -----
From: Eric Smith <eric_at_brouhaha.com>
To: <classiccmp_at_classiccmp.org>
Sent: Tuesday, April 18, 2000 12:44 PM
Subject: Re: 8-bit IDE

> "Richard Erlacher" <edick_at_idcomm.com> wrote:
> > Frankly, the reason I'm exploring this is because with the 8-bit mode, I
> > don't have to buffer the data at all beyond the on-board data-in and
> > out buffers at the bus interface.
> However, it doesn't matter if 8-bit IDE was standardized (at one time,
> but not any more), if there aren't any available disk drives that do it.
> It seems much more worthwhile to add the extra latch, buffer, and logic
> to make 16-bit IDE work, since then you can use readily available
> drives.
> This reminds me a little bit of the story of the main memory for the
> IBM 704 and 705 computers, as given in the book _IBM's Early Computers_
> (regrettably out of print). IBM had previously shipped the 701 and 702
> computers using electrostatic (Williams tube) memory, but it was found to
> be unreliable, so IBM was in the process of replacing it all with new
> core memory.
> Meanwhile, the product teams for the replacement computers, the 704 and
> decided to use electrostatic storage rather than core because it was
> The decision was overruled by Tom Watson Jr., who said something to the
> effect that choosing something that didn't work because it was cheaper
> something that did was the damndest business decision he'd ever heard of.
> Of course, if IBM was structured into separate profit centers for new
> computer sales vs. repair, you can see why the managers for new computer
> sales would make that decision. Pacific Bell does the same sort of stupid
> stuff. Installers will routinely steal working and in-use pairs from one
> customer for new service for another. It makes their statistics look
> and repair service is stuck with fixing the original service, which isn't
> the installer's problem.
> Eric
Received on Tue Apr 18 2000 - 16:16:37 BST

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