From Newsgroup: comp.sys.apple2

robsgreenneon@startmail.ca (Rob Jones) wrote in message news:<bc4b97a8.0410011839.4483998@posting.google.com>...

( ... )

Can this be done?

~Rob J.

You seem to have over simplified the description of what you are
trying to do: Apple Disk ][ drives, and Disk ][ compatible drives,
such as the Elites, although very simple mechanically, are a
complicated software-wise. Woz created a very simple drive, but
required software timing to synchronize the data stream: for one, it
does not use the sectoring hole in the disks to indentify the
beginning of each track's 1st sector. To synchronise with the start of
a sector, it must "bump" the head against the stop (grinding noise we
hear when head re-aligns itself), then very slowly advance the head
looking for a very specific sequence of data. Once this is found, it
now know where Sector $00 of Track $00 is and the drive must calculte
the position of the next track, taking into account the speed of the
drive, and the format (13-sector or 16-sector).

You have Elite drives: Use your software to format them into
Double-Density drives; If you have and Elite 3, you can define this
one as a DS/DD drive which will hold 560K.

My $0.02.

Robert.
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From Newsgroup: comp.sys.apple2

Robert C. wrote:

<snip>

To synchronise with the start of
a sector, it must "bump" the head against the stop (grinding noise we
hear when head re-aligns itself), then very slowly advance the head
looking for a very specific sequence of data. Once this is found, it
now know where Sector $00 of Track $00 is and the drive must calculte
the position of the next track, taking into account the speed of the
drive, and the format (13-sector or 16-sector).

Although I agree that what Rob proposed is more difficult
than he describes, your description of the operation of an
Apple drive is a couple of facts sprinkled liberally with
misconceptions that should not be spread.

First, when the drive recalibrates by seeking into the track
0 stop, it has then successfully found track 0. It will never
seek away from the stop to read track 0.

When it reads _any_ sector (not just sector 0), it scans the
disk data being read for a sector address mark, and then
the correct address information. After it finds a match on
the sector address, it reads or writes the sector data
immediately following (also enclosed in special marks).

All tracks are located open-loop, by stepping the correct
number of "phases" from the current position, referenced
ultimately to track 0, located by the track 0 stop. The
track value included in the sector address mark serves
as a check that the correct track is under the head, but
it is not used to do relative head positioning. If the head
is found to be incorrectly positioned, the drive recalibrates
to the track 0 stop as at boot time, and again moves the
head, open-loop, to the desired track.

The head is actually moved at a variable rate, accelerating
from a stop, seeking at a relatively high speed, and then
decelerating as it approaches the target track. This track
positioning is controlled entirely by the RWTS software,
and is both faster and more sophisticated than the constant-
speed stepping of hardware-controlled drives of the period.

Track positioning (for a standard disk, as opposed to a
copy-protected disk in non-standard format) is the same
for both 13- and 16-sector disks.

The Disk ][ system is both more sophisticated and more
efficient than your description suggests.

-michael

Check out parallel computing for 8-bit Apples on my
Home page: http://members.aol.com/MJMahon/
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From Newsgroup: comp.sys.apple2


"Michael J. Mahon" <mjmahon@aol.com> wrote in message news:20041003191054.13148.00002057@mb-m28.aol.com...

Robert C. wrote:

The Disk ][ system is both more sophisticated and more
efficient than your description suggests.

Back in the day (][/][+ era), there were a couple of static drives that emulated the Disk II. A coworker has one in his collection though he hasn't powered it up since 1983 I bet. He said he spent $700-$800 on it back then.

I'll ask him about it, see if he has the manual - I think he said he did. I think SCRG made one, and Vista...


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