Re: MISC
>Well - if you look at them closely it becomes obvious that
>the six machines are after all just flavours of two ideas.
>
>1) The move machine
>2) subtract, branch
>
>The mentioned "subtract" machine is a combination of both.
>
>However I dont really consider 1) as a one instruction machine.
>After all it is just a fancy way of doing microcoding. A move
>to the PC is after all not just a move, but a JMP. And thus
>you already have two instructions. The same goes for the ALU
>stuff.
Bear in mind that the PC doesn't have to be an actual register. A good
example of this is the PDP-5, which stored the PC in location 0.
Executing an instruction began by fetching location 0 and using it as
the address of the instruction to be executed. It was possible for a
DMA device to cause a jump by writing to location 0; this was, in fact,
how the front panel loaded an address into the PC.
--
Roger Ivie
rivie@teraglobal.com
Not speaking for TeraGlobal Communications Corporation
