EDSAC on your desk.

From: Eric Smith <eric_at_brouhaha.com>
Date: Tue Sep 22 19:51:04 1998

I wrote:
> Yes, but as part-owner of a DECsystem 1090, I can assure you that storing
> it is only a small portion of the problem. Powering it and cooling it are
> very problematic. It wants around 8 KW (3-phase 220V at over 35A). And

Tony Duell wrote:
> Remember I'm in the UK -- 240V mains, and 30A ring mains are common. In
> other words running it from time to time would not be a major problem. I
> suspect my 11/45 pulls half that amount of power, for example, with all
> the peripherals I have on it.

The KL10 draws over 8 KW for the CPU card cage alone. That doesn't even
include the memory or memory adapters, I/O channels, PDP-11/40 front end, and
DECtape that happen to be in the same three-bay cabinet. The CPU is not
capable of executing a single instruction without all of this support.

It also does not include any disk drives, 9 track tape drives, or
communications system, all of which are necessary for it to function as
a usable system.

You may have 240V mains, but it's split phase, isn't it? The KL10 *needs*
three phase - the first stage power supply for the main CPU card cage
uses a three-phase rectifier arrangement to get I-forget-what DC voltage
(and I'm too lazy to lazy to calculate it). This DC voltage is then used
as input to the second stage. The end result is ten outputs of 5.2VDC at 35A,
and four outputs of 2VDC at 35A. A substantial portion of the 8KW is
converted to heat just in the power supply; only 2100W is actually available
to the logic.

I'm considering converting the machine to use switching power supplies,
as was done by Compuserve. Using VICOR modules, this would take five
front-end modules and fourteen DC-DC converter modules, for a cost of
around $2000. However, it would make the machine much less expensive to
operate. With this change, I thing it would be possible to power it from
a typical US electric range or clothes dryer circuit.

However, RP06 drives are another matter entirely. They need three-phase
power for their motors. I'm reluctant to try the capacitor trick.

Eric
Received on Tue Sep 22 1998 - 19:51:04 BST