[sebhc] Re-creating actual floppies from archive
leeahart at earthlink.net
Tue Mar 14 19:27:41 CST 2006
Joe Smith wrote:
> All those images and no way to turn them back into disks? That is
> basically what I want to know, I don't really see anything that
> lets you do that.
Heath's standard disk distribution format was 5.25", single-sided,
single density (about 90k per disk) for *both* hard-sector (H17) and
soft-sector (H37) controllers. Obviously, the soft-sector controller
could store a lot more by using double- or extended-density and/or
double-sided. But keeping the same single-density format made it easy to
put your master distribution files on a disk -- both have the same
layout; same tracks, same sector size, same number of sectors.
I think that the Heath format puts the sector numbers *in* in sectors;
thus interleave doesn't make any difference in the data read; just the
physical position it has on the disk. The operating system says "read
sector 1." The disk controller keeps reading until it finds sector 1 and
reads it. The sectors might start anywhere, and go by in any order. Then
the operating system says "read sector 2", and the process starts again.
Interleave is just a way to arrange the sector order so sector 2 happens
to just get to the read head as the controller starts that read sector 2
command. Thus the time delay is minimized. If the controller is slow
(for example, a 2 MHz 8080 and the software was written for a 4 MHz
Z80), all that happens is that the disk controller has to wait a full
revolution for sector 2 to come around again.
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net
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