On Tue, 7 Jul 2009, Chuck Guzis wrote:
Well, yes and no. The Kaypro formats, at least in its
non-Advent ROM
incarnations, 10 512-byte sectors per track, leaving out the IDAM on
each track. The NEC 765 and its derivatives go blind for a period
after the index (the original 765 and 8272 are blind for longer than
the later versions of the chip) long enough to avoid seeing the IDAM.
I think this is wrong. First, noone needs the Index Address Mark, second I
can read my Kaypro II and Kaypro 4 disks without problems on an old 1986
HP Vectra with ?PD765 FDC. At least ImageDisk doesn't seem to have any
problem with these disks.
The Kaypro disks are 10 sectors/512 bytes per sector.
The Kaypro uses an interleave of 1:4 with sectors numbered
0,8,3,6,1,9,4,7,2,5; the Kaypro 4 uses DS disks and continues with
10,18,13,16,11,19,14,17,12,15 on the other side.
The problem with the Kaypro is that there is no IDAM
on Kaypro-
formatted diskettes, so the IAM of the first sector isn't seen and
only 9 sectors instead of 10 are visible to the 765.
The 765 does not need the IDAM. And the original IBM floppy format (3742
and System/34) doesn't even mention an IDAM. Personally I have not seen a
system that actually needs an IDAM.
Christian