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Re: After 20 Years, I'm This Close To Finally Escaping Data Rot -Thoughts?



winston19842005@yahoo.com wrote:
On Feb 25, 9:30 pm, "Bill Garber" <willy4...@garberstreet.com> wrote:

"D Finnigan" <dog_...@macgui.com> wrote in message

dog_cow-1267150605@macgui.com">news:dog_cow-1267150605@macgui.com...


Michael J. Mahon wrote:

Just out of curiosity, what is the technique for making a
second index hole in the jacket without damaging the media?

I noticed that many of the disks which I inherited had
been punched with a standard, hand-held paper hole punch.

You may be referring to the Write-Protect Notch.
The hole we are referring to is the small hole
near the hub which sets up the start of each track
on some drives. Apple disks don't actually use it,
but, if it isn't there on the flip side when trying
to read it with an IBM drive, it won't work.



They didn't use it at all? Now thinking back, I remember the TI-99
only uses it for the format routine, and thereafter there is an index
pulse/start of track on the disk placed by the format routine.

No, the Apple drives (made by Shugart) didn't even have the sensor
installed.  Instead, the formatting software writes considerably more
than a track on track 0, then reads it back to determine the actual
track length, adjusting the sector gaps appropriately to provide the
desired number of sectors and safety margin for drive speed variations.

It is never needed for operations on formatted disks, since each sector
contains its track and sector number, and the address header is read
prior to any data reads or writes.

-michael

NadaNet and AppleCrate II: parallel computing for Apple II computers!
Home page: http://home.comcast.net/~mjmahon

"The wastebasket is our most important design
tool--and it's seriously underused."