On a sunny day (Sat, 7 Mar 2020 16:06:39 -0000 (UTC)) it happened Martin
Gregorie  wrote in :

>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.

These days it is AFAIK all done in digital memory,
at least that is how I do it on the PC, you can do it too:
 mplayer -fps 2 video.avi


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

Yes! Nice! Seen similar setups at IBM.



>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.

Thanks, sometimes it is nice to see the old days..

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