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From: cyliao@eng.umd.edu (Chun-Yao Liao)
Newsgroups: comp.sys.apple2
Subject: Re: DOS 3.3 Question
Message-ID: <1990Apr11.193838.14208@eng.umd.edu>
Date: 11 Apr 90 19:38:38 GMT
References: <9004091826.AA14659@mrcnext.cso.uiuc.edu>
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Organization: Maryversity of Uniland, College Park
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In article <9004091826.AA14659@mrcnext.cso.uiuc.edu> alfter@MRCNEXT.CSO.UIUC.EDU (Scott Alfter) writes:
>So what you're saying is that disk space isn't currently being as efficiently
>used as it could?  I'm forever seeking ways to jam more than 140K on a disk.
>Apple's newer drives (DuoDisk, Apple 5.25, IIc internal) are supposed to handle
Nope, I believe that's the only way to assure your data not to be disturbed
by writing next to the data track. Remember, the Apple 5.25 driver's head is
just TOOOOOO wide that actually covers entire 1/4 track and usually spread to
1/2 track.Therefore, you need at least 1 full track of distance between each
data track. (remember, writting to the track 5 will intefere data on track
5.5 and 4.5, writting on track 6 will interfere data on 5.5 and 6.5, so if
you try to write the data of track 6 to 5 3/4 track, then it will intefere
track 5.25 which is right under the head if reading track 5. See, you MUST
leave 1 full track of distance between each data track.)

>38 tracks with no problem (I have a DuoDisk), and the Disk II (and most of the
>drives modeled after it) are supposed to take a full 40 tracks.  Why settle on
>a piddly 140K when you can get 152K?  Your comment raises another possibility,
>though.  If three-fourths of a track is a safe spacing, then even on the newer
>drives it should be possible to get 50 of the 3/4-tracks, for 200K on a side!
>Biggest problem here is that while you only have to poke one byte and fix the
>volume bitmap to get ProDOS to accept more than 35 tracks, it would take a 
>major MLI hack to deliver 200K--not to mention that it would probably end up
>breaking the current format unless there's room for almost a whole new driver
>in ProDOS 8, and a way to distinguish between the "extended" disks and normal
>disks.  (Anyone at Apple care to comment on this?)  Besides, I can't figure out
sure, you can easily modify the dos to use extra tracks (just few bytes, or
one byte? I don't remember) but again, you can't use 3/4 track.

>how to get anything less than half-tracks; you say quarter-tracks are a mess
>to get from the drive.  Just what is involved in quarter-tracking?  I have
>some material on how 5.25" drives work (including Beneath Apple ProDOS), but 
>their documentation would have you believe that only half-tracks are normally
>possible.  (I have seen quarter-tracks in copy programs, though.)

yes, but newer half-high drivers can handle 1/4 track without problem. It 
involves the control of step motor. You make step motor's magnet to move
the head by 1 hard track (1/2 data track) , but activate the magnet to move
it back at same time.  In this case, the head receive the force of magnet 
at same time so it stay at somewhere half way to each hardware track, that's
1/4 data track and the socalled quatertrack. You can use your manual to 
figure out how to control step motor.




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