On Sat, 07 Mar 2020 11:55:45 +0000, Jan Panteltje wrote:

> There is a history, in around 1968 to 1976 I worked as technician for
> the national broadcasting network here, bit like BBC in the UK.
> In the 1975? or so we had slow motion machines that used BIG disks, the
> Ampex HS100, it had 4 heads on 2 disks, one head recording one head
playing back the same time,
> changing and cleaning platters had to be done on occasion:
>  https://www.youtube.com/watch?v=cW7jvmoLQ7o
>
Interesting stuff - never knew how video slomo worked before.

Just found this:

http://www.chilton-computing.org.uk/acl/technology/1906a/p005.htm

If you scroll down, the 3rd picture shows an EDS 60 disk pack (60MB disk)
being exchanged on a disk drive.  The drive in that picture is a slide-
out unit, which I never saw.

The 8th picture shows a free-standing disk drive, which is the type I'm
familiar with - the lid hinges up for access when you need to change the
disk.

To remove a disk pack, the clear plastic cover fits down over the stack
of magnetic platters. You screw the handle down to lock the pack into the
cover and release it from the drive spindle and then lift it off.
Finally, you screwed a flat plastic cover on the bottom to keep the disk
pack in clean conditions when put in storage.

When the pack is on the drive and running a cover closes over it and
filtered air circulates round the spinning disk. There's a servo-driven
rack of heads, one per surface, that bangs in and out for access to data.
The servo used an optical indexing system (not part of the disk pack) to
locate recording tracks. The read/write heads all fly, just like modern
HDD systems.

Unlike modern systems, if the mainframe was running UDAS, there was
typically a different set of disks for each set of programs, so when
switching from, say, invoicing to payroll, the first job was to change
the disks take off the disks containing the onvoicing programs and data
and replace them with the payroll disks. UDAS was a tiny, in-memory OS,
so didn't care which disks were on the drives.

Drives were heavily partitioned. In modern terms, each file occupied its
own partition, so part of the system designer's job was to define the
number, size and names of the disk files needed my the new system, and to
place them on disk to minimise head movement because that was much slower
than accessing data on the same cylinger (slang for the same numbered
track on all surfaces).

If the box was running George 3, things were quite different: George
usually owned the at least one whole disk and managed a dynamically
assigned, hierarchic filing system on them - very similar to Unix/Linux -
except that all files and directories were automatically backed up to
tape. Files that weren't recently used could be, and often were, erased
and the space reused. If the file's owner now needed it, no problem,
because George asked the operator to load the required backup tape and
copied the file back to disk.

Right: quite enough of that: I now return you to your normal programme.


--
Martin    | martin at
Gregorie  | gregorie dot org

--- SoupGate-Win32 v1.05