On May 31, 2014, at 7:29 PM, Chuck Guzis <cclist at sydex.com> wrote:
On 05/31/2014 09:14 AM, Paul Koning wrote:
IBM didn?t do that on other machines, though.
For example, the 1620
had 200 digit sectors, if I remember right.
And a group mark, so sectors were pretty much anything from 1 digit to 200 digits in
Yes and no. Yes, the group mark would act as the logical end of data mark, ending the
read instruction. But the physical sector size was always 200 digits.
By contrast, the 360 disk format would actually write physical blocks the size you asked
sizes were found in other machines of that era as well;
the CDC mainframes had sectors of 322 12-bit words, which were
usually exposed to the programmer as 64 60-bit words, reserving the
first 24 bits for file system control purposes. (PLATO, early on,
did make all 322 words visible because it had its own file system,
but at some point that became a nuisance and there was a whole system
file conversion from 322 to 320 word blocks.)
Was it the 853 disk drive that was set up to take either IBM-compatible hard sectored
packs as well as the 6000 version of the packs with different sectoring? I seem to
recall a 1SP overlay that would allow 853 IBM-type packs to be used on a 6000, but with a
considerable loss of capacity.
I?m not familiar with those ? only worked on 844 drives, which DEC users know as the
The format of those packs was established by a low level micro-engine in the disk
controller (7054). I suspect that could handle a wide variety of formats just by
reprogramming the ?controlware?. Should take a look; I have a copy (but no longer any
manual for that processor).