Re: AE HD+ driver

[mjmahon@aol.com (Michael J. Mahon)]

Wayne Stewart replied:

>Bart wrote:
>
>> In answer to what it is: The AE HD+ is a Applied Engineering 3.5 Floppy that
>> was made briefly.  It is similar to their standard 3.5 clone only with 1
MAJOR
>> difference: It supports 800k AND 1600k  disks.  Yes, 1600k.  This is
>> accomplished via a special format they developed (its GCR not MFM) and the
>> interaction of a GS/OS driver and a special EPROM they programmed for the
>> logicboard of the drive.  My drive was recently aquired from Goodwill with
the
>> case slightly wraped out on 1 side, non working and with a wire hanging
loose
>> so, I took it apart.  I plugged back in the wire, blew out the crud with
canned
>> air and found...  The reason it was warped  and messed up was someone
>> had been in here before and...took the EPROM.  dang it!
>> I therefore seem to have a standard 800k AE drive with a cool looking case
>> marked AEHD+  So it goes.....
>
>I have the AEHD 3.5 which does all that. Also works as a 1.4mb if hooked up
>to a Superdrive controller. I took a look, no EPROM inside though.
>Question is, what's the difference between the AEHD and the HD+ ?

Sounds like that 24- or 28-pin socket may not have held an EPROM, but
a gate array of some kind.  Wayne could verify that, since his drive is
almost certainly very similar.

The 1600KB format is just Apple GCR with twice as many sectors per
track (number depending on zone).  This is accomplished by doubling the
data rate, which should be automatic with HD disks.  Making RWTS work
would take a few changes, but nothing drastic.  The real issue is getting
an IWM chip to run at double data rate.  I expect it would work if clocked
faster, but it would certainly tighten up the margins for grabbing the data
bytes, unless this is done by hardware (and buffered in an SRAM).

All in all, a lot of trouble to get another couple hundred KB on a disk,
compared to 1.44MB at constant speed and fixed sectors-per-track.
Of course, this also requires hardware data capture and buffering,
as in the SuperDrive Controller.

-michael

 Email:  mjmahon@aol.com
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