7 Apr
1999
7 Apr
'99
3:54 p.m.
The disk drive has a place beyond which its head assembly won't move. If
you've ever written FDC code, you know what it sounds like when you try to
go beyond the limit. What's more, there's a sensor to tell you when you're
at that point, though I doubt Apple used it. It's just as easy to move the
heads until you're sure they've gone as far as they can. Once you've done
that, what better way could there be than to look for a track and then
adjust until the signal is readable? That's how drives of all sorts work
today. Of course, they all have some way of establishing where a track
ought to be to begin with.
Dick
-----Original Message-----
From: Max Eskin <max82(a)surfree.com>
To: Discussion re-collecting of classic computers
<classiccmp(a)u.washington.edu>
Date: Wednesday, April 07, 1999 8:53 PM
Subject: Re: stepping machanism of Apple Disk ][ drive (was Re: Heatkit 5
1/4 floppies)
On 8 Apr 1999, Eric Smith wrote:
>> These fellows
>> spent a couple of sessions talking about and demonstrating the screwy
means
>> by which certain game vendors in the Apple
market were "protecting"
their
>> wares by altering the timing of the
positioning routine, thereby making
it
>> possible to write tracks "off the
track" by changing the time delay
between
>> a known cylinder position and the point at
which the specific track was
to
>> be written. This made it impossible for
someone using the stock timing
of
> the
positioning mechanism to read the diskettes so written.
How does this work? Do you mean that the disk drive has no internal means
of judging whether or not it's on the right track and that this is
determined by the contents of the disk?
--Max Eskin (max82(a)surfree.com)
7 Apr
7 Apr
11:28 p.m.
you've ever written FDC code, you know what it
sounds like when you try to
go beyond the limit. What's more, there's a sensor to tell you when you're
at that point, though I doubt Apple used it. It's just as easy to move the
Actually there are two points. One is track 000 and the other is the
innermost (for sa400 35-40 tracks later). Only track 000 was sensored
save for apple didn't use that either. Apple cut the interface to the
minimim number of wires and signals possible and made up the difference
with software, rather clever in my mind.
Allison
8 Apr
8 Apr
12:41 p.m.
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3:37 p.m.
On Thu, 8 Apr 1999 allisonp(a)world.std.com wrote:
Actually there are two points. One is track 000 and
the other is the
innermost (for sa400 35-40 tracks later). Only track 000 was sensored
save for apple didn't use that either. Apple cut the interface to the
minimim number of wires and signals possible and made up the difference
with software, rather clever in my mind.
During the design phase, Woz had more time than money, chips cost money
and software only cost time. Remember that he _wanted_ to use the 8080
but the 6502 cost only a tenth the price. (Imagine what the Apple
might have been like with a decent CPU from the start).
--
Ward Griffiths
"the timid die just like the daring; and if you don't take the plunge then
you'll just take the fall" Michael Longcor
7:47 p.m.
During the design phase, Woz had more time than money,
chips cost money
and software only cost time. Remember that he _wanted_ to use the 8080
but the 6502 cost only a tenth the price. (Imagine what the Apple
might have been like with a decent CPU from the start).
It may be hard to imagine now the typical processors are about a thousand
times faster than the first 6502 Apple used, but the CPU was not the weak
point of the system, it was slow or limited peripherals. Only later when
the IIgs became weighted down with GUI etc. did the cpu start to lag the
rest of the system.
9219
days inactive
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4 comments
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participants (5)
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allisonp＠world.std.com -
ard＠p850ug1.demon.co.uk -
edick＠idcomm.com -
gram＠cnct.com -
mikeford＠netwiz.net