Wtd: ESDI 3.5" hd + hd ?'s

From: R. Stricklin <red_at_bears.org>
Date: Tue Jan 6 15:15:23 1998

On Tue, 6 Jan 1998 jpero_at_cgo.wave.ca wrote:

> Spits out water! What? I have seen exactly like that, uses driver
> on an bootable mac disk to talk to that hd via serial port.
> ZZZZZZ.....what? program loading done? hummpth... once again
> Click, tap tap click to do someting...yawn!....
> waiting form some thing to exhange stuff around between two. :)

Speaking of the Apple HD20, an external 20 meg hard disk for the Mac
512k. Since the machine it was designed to be used with does not sport a
SCSI bus, it plugs into the floppy port. According to Apple, it is
supported on the 512k, 512ke, Plus, and SE. Since these are the machines
that support the 400k floppy drive, I suspect that it would also work on
the 128k barring any memory shortages, although I haven't been able to
test this yet. Apple can't decide whether or not it's supported: here it
is, there it isn't.

It cost over $1000 new in 1986 (although I believe it was introduced
sometime in 1985). Inside is a 3.5" HH Rodime 552 disk, which actually has
an Apple Disk Drive interface right on it. I had expected some sort of
conversion circuitry (like the old Sun ESDI->SCSI boards), but there

  Average seek: 415 ms
    Rotational: 394, 429, 472, 525, 590 RPM
Burst transfer: 489.6 Kbits/sec (serial)

  Average seek: 85 ms
    Rotational: 2744 RPM
Burst transfer: 500 Kbits/sec (serial)

It looks like the 500kbits/sec is a limitation of the floppy interface and
not of any device on it.

Anyway, since the 512k only knows how to boot from the internal floppy,
and speaks only MFS (the original, flat Mac File System---the folders are
purely ornamental! Stupid trivia bit: folders on MFS disks have one extra
pixel) on a 400k disk drive, Apple got creative with their solution:

The Apple HD20 INIT (introduced with System Software 1.1) patches the ROM
to allow the use of HFS (a 20 meg flat file system would be a horrible
mess), the HD20, and the 800k disk drive.

Insert the boot disk with 1.1 and the HD20 INIT, the Mac boots half-way,
spits out the disk, and continues from the HD20. Kind of neat.

On the Plus (and presumably 512ke), which speaks HFS and 800k disk drive
natively, you can boot right off the HD20. But the Plus has SCSI, so this
is trivial.

				 r e d   _at_   b e a r s . o r g
				 [ urs longa  |  vita brevis ]
Received on Tue Jan 06 1998 - 15:15:23 GMT

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