Your target of the technology of 1963 fits reasonably well with my
1962 mainframe, it uses drum(s) for backing storage (holding program
and data overlays to be brought into core) but I don't think that
makes much difference to the drum itself, other than you may want
more than one read/write head per track.
Each drum looks to be about a foot diameter and about a foot and a
half long. They spin at 5240 rpm on a vertical axis. The drum is made
of aluminium and the manufacturers (International Computers and
Tabulators) had a lot of trouble getting the surface coating right,
trying all sorts of high tech methods until they found the most
effective method was for someone to smooth it on by hand while the
drum was spun at low speed, rather like a potter throwing a clay pot.
They also had problems with the length of the drum, and had to
logically divide it into two sections, each one with its own timing
track and datum track. Hopefully if you keep the drum length small
this will not be a problem for you.
The drums are powered by 3/4 horse three phase motors with V-belts
providing a step UP in speed from just under 3000rpm at the motor to
5240rpm.
They do not need clean room conditions, they are not sealed, and even
have a fan to draw cold air up from the bottom over the surface and
out the top, or is it the other way around, I can't remember, the fan
are currently removed anyway and the drums run fine in a rural
environment (i.e. reasonably clean air, no coal fire smoke/smog/
diesel particulates)
The drum sits within an aluminium casing which holds 244 (+some
spares) read/write heads arranged in a helix so they do not need to
be physically close to each other.
The heads do not fly, and can be moved in and out using an Allen key,
which is apparently done whilst watching a pressure gauge on an
airline blowing air through a venturi in the read/write head, so that
when the air pressure reaches a certain level, the head must be close
enough to the drum because the drum is starting to impede the air
flow. The steel screws have now rusted and seized in the aluminium
but work just fine because if can't work loose they can't go out of
adjustment.
The drum is coated rather than plated, I know this because when
certain machines used by the Home Office for security purposes were
decommissioned, a friend of mine was required to dismantle the drums
and wash the magnetic coating off of the drums before they (the
drums) were allowed to leave the premises. The machines had earlier
survived being blown up by terrorists detonating a bomb on the window
ledge outside one of the computer room windows. They don't make them
like that any more, tough as old boots!
The same friend also worked on a serial drum machine with valves
which was installed at a Carbon factory where the inside of the
machine used to get covered in conductive fine carbon dust. It is
amazing it worked at all. Another friend worked on modern electronic
weighing equipment at a phosphate factory using bird droppings as the
raw material. He was called in to one machine which had stopped
working the previous day, and found a small rubber grommet had
failed, the chemicals had got in and eaten the resin of the PCBs and
the copper tracking was hanging loose inside the cabinet, it seemed
that it had somehow been working in that state for some time because
it would have taken some weeks for the resin to be consumed, so maybe
this contradicts my statement that they don't make them like that any
more.
The 1MHz main machine clock is derived from the 250KHz drum timing
track, so no need to synchronise to the drum except when switching
between drums, or the two halves of a drum.
The machine can also be run from a separate clock, though of course
all drum accesses fail. For fault finding, it can even be run one
cycle for every time you press a button, wonderful to watch data
shifting through the registers displayed on the front console and see
where your data is getting corrupted. Not so good for fault finding
the drum, magnetic tape or other peripherals though.
I hope some small part of these details might be of help to you, good
luck with the project.
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