8-bit IDE

From: Richard Erlacher <edick_at_idcomm.com>
Date: Sun Apr 16 18:19:21 2000

Those "special" drives are not what I meant to ask about. I want to know
more about the 8-bit mode described in the ATA Interface Specification as
published in 1994 and 1996. This is apparently a "standard" feature.

It appears that there's a control bit in one of the control registers that
allows the interface, which defaults to 16-bit mode, to be configured for
8-bit data width.


----- Original Message -----
From: Tony Duell <ard_at_p850ug1.demon.co.uk>
To: <classiccmp_at_classiccmp.org>
Sent: Sunday, April 16, 2000 12:05 PM
Subject: Re: 8-bit IDE

> > Recently, as part of my effort on an S-100 "hard-card" using a 2-1/2 =
> > inch ide drive, I've been revisiting the 1994 standard for the ATA =
> > interface. There's a not-too-detailed mention of an 8-bit mode which is
> > set up using a bit in register. This feature was apparently obsoleted =
> > as of 1996's standard. =20
> I remember _special_ 8 bit IDE drives. The model numbers usually had an
> 'X' (for XT, I guess) in them, and they were used with special 8-bit
> controller cards in PC/XT systems. I have no idea how compatible the rest
> of the interface was with the PC/AT IDE drives. These drives are almost
> impossible to find now, at least in any quantity.
> It's actually not that hard to use a normal 16 bit IDE drive in an 8 bit
> system (like an S100 card). You need a few buffers/latches to convert
> between 8 and 16 bits on read/write, that's about it.
> Actually, although it pains me to say this, IDE drives are so cheap per
> megabyte now that you could probably get away with wasting every other
> byte... Just use a 3-state buffer to always write the top 8 data lines as
> 0 (or FF or...) and ignore them on read. After all, people give away 1Gb
> IDE drives these days (or so I've heard), and 500M of storage (i.e.
> wasting every other byte) is massive for S100 systems.
> -tony
Received on Sun Apr 16 2000 - 18:19:21 BST

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