Re: Reading old 3.5 CP/M diskettes using an actual USB floppy drive?


"Aly" <,shfskfjsf@xxxxxxxxxxxxxxxxxx> wrote in message
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"Juergen Marquardt" <marquardt@xxxxxx> wrote in message
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< SNIP >
out, and piecing it together sector by sector.

Mine went something like 1,12,2,13,3,14,4,15,5,16 etc.

comp.os.cpm may be worth a look in. They have experience of this.

And what makes it EVEN MORE FUN!! is that different builds of CP/M lay
down
the sectors in completely different ways. :-)

Back in the olden days this was called sector interleaving, and as best I
remember, used only on soft sectored disc drives. It was a technique to
synchronize "high speed" hardware (instructions often took many microseconds
to execute) with those slowly revolving mechanical discs. Most machines
were optimized to have the interleave factor set to make the hardware
read/write the disk in as few rotations per track as possible. Some could
only do one sector per revolution, others 2 or more. The disk controllers
of the period usually required programming on a sector by sector basis. Ah,
the good old days.

Regardless of the interleave factor, the disks were compatible from machine
to machine (presuming both machines had the same density, number of sides,
etc.) because the sector number was contained in the sector header.
Performance might vary widely because of differing interleave factors, but
the data would be read/written in the correct sectors.

Thanks for the memories
Scott


.

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