Reply to post: Re: Apple ][ drives (Was: Put a heater in the safe then ?)

Haunted disk-drive? This story will give you the chills...

SImon Hobson Silver badge

Re: Apple ][ drives (Was: Put a heater in the safe then ?)

Woz had the genius idea of saving 5c on the cost of each drive by deleting the track zero sensor. ... the computer would smash the heads against the track 0 stop 39 times.

Actually, no it didn't. I think you'll find it was only 10 times (only one of four steps on the stepper would be pushing against the stop), and it could have been less because (from memory) they ran the heads out first - so you'd hear the swish and potentially clicking as the needle skipped in the groove - before it ran back and made a few taps.

And it wasn't the heads against the stop, it was a part of the carriage specifically arranged to engage with the head positioner scroll disk.

This feature / abuse provided Apple service centres with a regular income stream; customers had to present their drives to have radial alignments performed at regular intervals.

Really ? I never once had to have mine done, and I don't know anyone else who did.

But that was really just a minor cost saving. What really saved a lot of money, and showed what a genious Woz was, was how he replaced a couple of VME boards full of chips with just 1/2 dozen chips and a state machine ROM - plus some software. I recall the size and complexity of the two VME boards that formed the controller for the external drives on our Intel MDS at work (not to mention the racket the 8" drives made with their head load solenoid) - and the simplicity of the Apple controller I had at home.

And the creative way he found a better coding and was able to upgrade from (IIRC) 13 sectors/track to (IIRC) 16 s/t with nothing more than updated ROMs (replace P5 and P6 with P5a and P6a) with fresh code and a new state machine.

Ah, this takes me back a bit. Oh those days when 48k (or if a showoff like me, 64k) was considered a lot of RAM and was enough to do useful work. Not to mention the hardware being simple, and slow, enough to easily build your own stuff from a few TTL chips.

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