Re: More than 256 sectors per track?

From: Marko Mäkelä (
Date: 2001-08-16 13:07:59

On Thu, 16 Aug 2001, Andre Fachat wrote:

> Instead of directly counting up or down I would recommend something
> like a binary search, like first searching sector 256. If it works, go
> up to 512 if not, down to 128. Repeat this until you have an upper and
> a lower bound.

Actually that is what I implemented on Monday evening.  I haven't had time
to touch the stuff after that (I've been working on my thesis), but it was
pretty fast, probably less than 1 second/track when I let it swipe through
all tracks and find the number of sectors on a 1541.  For efficiency
reasons, I used 8-bit numbers, so it'll only work for up to 256 sectors.

I've been thinking about an optimization: what if the upper and lower
limits are fixed to, say, half and twice the number of sectors found on
the first track?  The search could converge a little bit faster in that
case.  But I think I'll implement just this simple binary search first.

I'll also simulate it with all possible outcomes, since I have bad
experience from an integer-math 2-base logarithm function I wrote.  In
that search, I set low=current+1 or high=current-1, and one of the
comparisons was so sloppy that a situation high<low was reachable.


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