1 Dec
2015
1 Dec
'15
9:43 a.m.
On Tue, 1 Dec 2015, Paul Koning wrote:
On the subject of DECtape, and "keeping good
track of things" -- DOS
format DECtape has 510 bytes per tape block, the other two bytes are
used as the link word. It's a bit like MSDOS FAT format (or CDC 6000
series, which did it 20 years earlier), but with the links in the blocks
rather than in a separate region. The directory points to the first
block, and you get the next block address when you read the first.
Take a look also at Apple-DOS!
"Beneath Apple DOS" seemed to be the canonical reference to it.
IFF I'm remembering correctly, . . .
DIRectory on track 17.
256 bytes per sector.
Each sector within a file has 252 bytes of data and a 4 byte pointer to
the track and sector number of the next sector
GCR (with a different GCR pattern for the 13 sector V 16 sector disks)
It had a sector interleave, but inefficiencies in the OS (copying bytes
to and from a buffer) resulted in the need to change the interleave a few
times.
There are prob'ly some here who remember all of the details.
I had little to no experience with it, other than writing the file
system software to go with a crude flux-transition board ("Apple
Turnover") to copy files from 13 and 16 sector Apple DOS, Apple CP/M,
Apple Pascal, and Pro-DOS.
It never worked well.