31 May
2014
31 May
'14
9:14 a.m.
On May 30, 2014, at 5:38 PM, Tom Gardner <t.gardner at computer.org> wrote:
IBM famously introduced its CKD disk file format in
the 60s; did anyone else
(other than IBMs clones including RCA) support such a disk format?
Specifically a disk format with a block (record in IBM terms) having a
variable length key field (including 0 length) and a variable length data
field. To the best of my knowledge everyone else used a fixed block (sector
to most) size on a disk volume but my knowledge of most of the BUNCH is
limited.
I remember that from the 360s. That?s the only place I ever saw it. Variable length
records, varying even from one record to the next, egads. You could have 80 byte sectors
storing card image files, though you were encouraged to use longer sectors for efficiency.
Lots and lots of documentation about this in the JCL manual, and utilities for dealing
with format changes, and large amounts of complexity in the OS syscalls to specify all
that. It never was clear to me what the point was.
IBM didn?t do that on other machines, though. For example, the 1620 had 200 digit
sectors, if I remember right.
Funny sector 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.)
paul