Re: Edhel finds DOS 3.3 speed-up (was DOS 3.3 versions)

[dastar@crl.com (Sam Ismail)]

Neil Parker (nparker@cie-2.uoregon.edu) wrote:

: You *really* don't want to try accessing the disk drive when the disk is
: spinning at significantly less than full speed, as it will be if you cut
: too much time off the start-up delay.  Apple's disk controller is somewhat
: fussy about data timing:  bits are expected to come in at 4-microsecond
: intervals.  If the disk is spinning too slowly, then the bits will appear to
: be more than four microseconds apart, and the controller will insert extra
: bits that aren't really there, thereby corrupting the data stream.

: Writing to the disk under these circumstances can be especially dangerous:
: if DOS somehow manages to decode what looks like the right sector header when
: the disk is spinning too slowly, then the data will be written at that slow
: speed, possibly producing a sector which is completely unreadable at full
: speed.

While your technical explanation is perfectly accurate, your dire warnings
of impending doom are highly over-stated, as the worst that could happen
is DOS will not find a good prologue in time and will, worst case, attempt
a recalibration.  And I can't even see this as happening since DOS allows
more than enough time to identify a correct prologue before it recalibrates
the drive (at least 6-8 spins).

And as you point out...

: DOS does contain some protection against these problems...it won't start
: doing any sector reads or writes until it recognizes the correct sector
: header, which becomes increasingly difficult as the speed decreases.  If it

...the disk will never get corrupted because DOS always gets its bearing
by reading before doing a write.  I could understand your concern if he was
trying to speed up the drive motor, but messing with this parameter is
harmless, data-wise.

: But still, by making this patch, you're gaining the speed improvement at
: the expense of reliability.  The more you try to push it, the more likely
: you are to run into problems.

Like I said, absolute worst case would be a recalibration, in which case
you lose 2 seconds instead of the 1/2 second gain, but again I can't see
this happening.

: You're much better off just using ProntoDOS or some other fast DOS, and
: not trying to squeeze additional miniscule speed increases out of
: less-than-totally-reliable techniques.

I agree.
A
A

-- 

Sam
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