On Wed, 18 Aug 2010 23:39:20 +1000, Clifford Heath wrote:

(resend)
flipper wrote:
On Mon, 16 Aug 2010 20:15:09 -0700, John Larkin
0 (*octal* 0) was no-op on the PDP-8, and there was a short program
that filled all of core with 0, leaving it circulating around the 4K
memory forever.
How did the little program manage to write 0 on top of itself?

Probably by arranging for the last instruction executed to
overwrite itself.

I designed a similar program for the Z-80 once. It went into
the last 7 bytes of RAM, with the last executed instruction
being a stack-push of a 16-bit register which contained zero.
The program would fill all of memory with zero (halt instructions)
and then halt at location zero. Cute.

Except that zero is nop on z80.

Grant.

Clifford Heath.