16 Feb
2021
16 Feb
'21
11:43 a.m.
On Feb 16, 2021, at 2:38 PM, Mattis Lind via cctalk
<cctalk at classiccmp.org> wrote:
...
What is interesting is that it had variable record length. It was specified
during the format process which tracks had what number of records and their
size. The first track always had 40 bytes record since it was the INDEX
track. File allocation was on a track basis. In the INDEX file each file
then had a start track and stop track as well as information on how many
records there were in the file and what size each record was. Also the
number of records per track were included in the file specification.
I have never ever heard of such a scheme before.
/Mattis
I haven't, for floppies. But flexibility even more than that is found in IBM/360 disk
drives, where you get to write sectors of variable length, and you don't even have to
pick them ahead of time. Not to mention that those have keyed sectors, allowing you to do
primitive databases directly in hardware.
A similar but more restrictive scheme is the disk drives on the Electrologica X8 (2311
lookalikes, built by CDC I think) where you have a choice of 6 different sector sizes, and
you get to make the choice separately for each track, at format time. You can reformat
any track at any time.
paul