14 Nov
2000
14 Nov
'00
2:38 p.m.
ard(a)p850ug1.demon.co.uk (Tony Duell) wrote:
Just about every HP calculator since the HP71B has been based on a CPU
called the Saturn (OK, the HP6S and HP30S aren't). This chip has a 4 bit
ALU and external bus, but with 64 bit data registers and a 20 bit address
width.
Hi
We all agree that the i4004 was a 4 bit machine. It had
a 12 bit address on a 4 bit bus that sounds similar to the
HP one. The 4004 used register pairs, that doesn't make
it a 8 bit machine. It also used 8 bit instructions.
The bus does not define that it is a 4 bit machine. The width
of the ALU does. Not the instruction width and not the address
size or register size.
I agree with Tony.
IMHO
Dwight
Tony Duell skrev:
>> I don't think I could form any relationship to a 4-bitter, either. I
woul=
>Oh, there are a lot of them about. Of course it depends what you mean by
>'4 bit', but if that's the ALU/bus width, then the HP Saturn processor
(used
>in the 71B, 28, 48, 49, etc, etc, etc) is a 4
bit chip. And I certainly
like
those
machines (and yes, IMHO they are computers rather than calculators).
I have no idea what you're on about. =) Besides, a 4-bit address bus seems utterly,
utterly limited.
Who said anything about a 4 bit address? Address width != ALU width in
general...
The Saturn works with 20 bit addresses. Memory is 4 bits wide, so the
Saturn can address 1Mnybbles (or 512K bytes). Some modern machines
(HP49G, for example) have bank-switching hardware to extend this further.