The origin of the phrases ATA and IDE [WAS:RE: formatting MFM drives on a IBM PC]

Liam Proven lproven at gmail.com
Wed Oct 4 07:29:15 CDT 2017


On 2 October 2017 at 14:22, Jules Richardson via cctech
<cctech at classiccmp.org> wrote:
>
> Does anyone know why IDE/ATA even came about? I mean, why SCSI wasn't used?

Sure, yes.

It was cheap.

SCSI was expensive, and that was aside from any licensing issues. A
working SCSI bus effectively means 2 smart devices, communicating over
a defined _shared_ channel.

ST-506 was simple, dumb and cheap... like the IBM PC.

https://en.wikipedia.org/wiki/ST-506

As drive capacities grew, ESDI came along.

https://en.wikipedia.org/wiki/Enhanced_Small_Disk_Interface

I believe partly due to timing issues, some of the "smarts" of the
controller were moved from the disk controller card onto the drive
electronics -- but the cables were kept the same. (2 cables, 34 pin
control cable, with 3 connectors, shared by up to 2 drives; plus 2×
20-pin data cables, one per drive.)

Then most of the controller electronics were moved onto the drive, so
that no "disk controller" was needed any more -- the drive contained
the controller. Now the 2 cables were consolidated into a single
40-way cable, one end of which connected to the motherboard and the AT
bus. (The 16-bit bus from the IBM PC-AT, so called to distinguish it
from the 8-bit bus of the IBM PC.) The cable had 2 connectors for 2
drives, but they had to be jumpered to tell them which was master and
which was slave, and not all combinations worked, not in the early
days.

IDE was mainly an x86 PC thing at first. Later, the 2nd-generation
Acorn ARM machines had it, and the Commodore Amiga 1200 had an
on-board interface for a 2.5" notebook-sized IDE drive. Later still
Apple adopted it for its cheap home machines, the Performa PowerMacs.
In the early ones, I think the hard disk was IDE and the CD drive was
SCSI, and they still included a SCSI bus.

Around 1994 or so, I ordered some machines from Elonex intended to run
Windows NT 3.1. There was a substantial saving on ordering IDE models
instead of SCSI-equipped ones.

What I didn't know is that these had 540MB drives, and the IDE
definition only allowed for 1024 cylinders, 63 sectors per track and
16 heads -- meaning 528MB max.

These were not IDE drives, they were EIDE drives. Enhanced IDE.

NT 3.1 didn't understand EIDE. It couldn't do Logical Block
Addressing, only Cyl/Head/Track.

So to NT, the last 12MB of these drives was all bad blocks.


Returns and much argument followed. That got me a mention in
Microscope magazine, which later got me an interview at Dennis
Publishing and a job on PC Pro magazine. 21 years later, I'm a tech
writer at SUSE in Prague. Funny how life turns out.

Later, other limits came in at ~8GB, then at ~128GB, then a rather
different one at 2TB.

http://philipstorr.id.au/pcbook/book4/hdlimit.htm



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