[cctalk] Re: HCF [was: System 360 question]

[Paul Koning via cctalk]

> On Nov 4, 2024, at 12:15 PM, Mychaela Falconia <fal...@freecalypso.org> wrote:
> 
> Paul Koning wrote:
> 
>> On the "one word clear", I missed a detail.  I pointed out you get to
>> initialize the registers.  You can also initiate one memory word.  In other
>> words: choose two words in memory, and registers contents, such that
>> execution will give you a memory full of zeroes and a halted machine.
> 
> OK, *now* the problem has a clear solution:
> 
> 1) Write 000000 into memory word 015720;
> 2) Write 015720 [ MOV @-(PC),(R0)+ ] into the last word of system RAM;
> 3) Clear R0;
> 4) Jump to the last word of RAM where you wrote the 015720 instruction.
> 
> This solution does require that the system RAM be of certain minimum
> size.  Assuming power-of-2 sizes only, the machine must have at least
> 8 KiB of RAM, otherwise location 015720 does not exist.  What was the
> smallest RAM configuration on PDP-11?

Yes, that's the correct answer.

4 kW is the smallest PDP-11 memory I know of, though I don't have direct 
exposure to the T-11.

        paul