5 1/4" hard-sectored disk..

[Jim Battle]

Jim Donoghue wrote:

> I have some 5 1/4" hard-sectored disks that contain CPU microcode. They
> aren't 'formatted' with a filesystem, but are read with a simple board
> that contains some 9602's, a shift register, and a Z80. A dilemma:
> should I try to intercept the data from the board, write it to flash
> memory, and build a board to replace the whole Z80/hard-sectored disk
> thing, *or* try to build something to write the data stream out to
> another 5 1/4" disk. The Z80 doesn't care about the sector pulses - only
> the index pulse. So I could get away with a standard floppy instead of a
> hard-sectored one.
> 
> The disk thing would allow me to keep using the original hardware, which
> would be nice, but I don't know the first thing about attempting to
> write the data stream back to the disk. 
> 
> I have no backups of the microcode disk, and no way to replace it when
> it dies. Every time I fire the thing up I feel I'm getting a little
> closer to it's death...

Jim, if you want to build hardware, you can, but personally, it would be 
easiest to use a catweasel card -- they can read and write disks.  The 
next generation catweasel card is supposed to be better at handling hard 
sectored disks, but since you said the hard sectoring doesn't matter, 
any catweasel card should do.

It simply counts how many ticks of a 14 MHz (or other selectable 
frequency) clock occur between each flux transition and logs it into a 
RAM.  You simply would have to write a bit of software to step the head 
to the right track, capture a snapshot of one revolution, save the data, 
step to the next track etc. Then, put in a fresh disk and hand the 
catweasel card the flux reversal timing that was recorded and ask the 
card to write out a bit pattern matching the timings you've just given 
it.  If you have two disk drives connect to it, you can ping-pong 
between then and do the copy that way.

So you can make a clone of the disk without having to reverse engineer 
the disk encoding or format at all.

For the $90 or so that it costs, it has to be cheaper than your time to 
build something custom.