Rare Apples, eBay, Goodwill

[Dwight K. Elvey]

>From: "Eric Smith" <eric at brouhaha.com>
>
>Sellam wrote:
>> It would have if it wasn't decided that 80 or so synchronization bytes
>> were absolutely necessary between each sector.  I still don't quite
>> understand what reasoning went into that particular aspect of the
>> design.
>
>Suppose you format a disk on a Disk II that is 10% fast.  Now you stick
>the disk in a drive that is 10% slow, and write a sector.  The 342
>nibbles of the data field will take up the space on the disk that was
>formerly used by 417 nibbles on the disk, or the 342 nibbles of the
>data field plus 75 nibbles of the gap.
>
>And I've ignored the header and trailer bytes, and the new self-sync
>written in the gap and after the end, so it's actually worse than
>that.
>
>As it is, 80 nibbles of gap isn't quite enough to allow for +/-10% speed
>variation and leave still leave enough self-sync bytes, but if they
>reduced it, writing a sector might overwrite the address field of the
>next sector, rendering that sector unreadable (even though the data
>field of that sector would still be intact).

 Of course, when did you see a drive that is anywhere
near 10% off in speed? Even the older belt drives could
hold better than +-5%. 5% is over one strobe maker per
second ( for the older disk with stobe marks ).
 The newer drives with electronic commutating can hold
much better than that.
Dwight

>
>They couldn't fit 17 sectors without seriously compromising the
>allowable speed tolerance.
>
>Some copy-protected games crammed in more by writing one giant sector
>per track.
>
>Eric
>
>