Do-It-Yourself PDP-11 help!

From: Gordon JC Pearce <gordon_at_gjcp.net>
Date: Tue Feb 15 19:53:21 2005

Tony Duell wrote:
>>a Fourth Generation Systems memory board, with 18 41256s on it (512kwords?)
>
>
> No. 256K 18 bit locations (i.e. 16 bit words with parity for each byte).
> So 256kW

Actually, if I was anything like numerate, I'd be able to count, and if
I could count I would have counted 36 memory ICs. Bah.

>>broken, and a three-position switch marked "L.T.C. on/off". With this
>
> Almost certainly 'Line Time Clock'. The mains-frequency interrupt signal.
> For some unknown reason this was controlled by software on Unibus systems
> (a bit in an I/O device register), but by a swtich on Q-bus machines.

There are two wires going from a small transformer to the Baydel card.
Seems reasonable, then.

Gordon.
Received on Tue Feb 15 2005 - 19:53:21 GMT