Do-It-Yourself PDP-11 help!

[Gordon JC Pearce]

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.