hardware multiply/divide functionality in CPUs

Tony Duell ard at p850ug1.demon.co.uk
Tue Mar 8 12:57:25 CST 2011

> You forgot one.
> Northstar* S100 system had an optional FPB it did BCD math (ADD, SUB,
> MUL, DIV) for two operand of 2 to 14 BCD digits.  It was much faster than
> could be done with software in the Z80.

I 'forgot' many more than one, I can assure you. Thre was that AM9511 
chip that was interefaced to many machines (I have seen an Apple ][ card 
with it on). 

I am not sure that counts, though. It didn't really extend the normal 
processor instrcuton set, rather it was a periphral for doing arithmetic.

> EAE was PDP-8

Maybe I've mis-remeebred the name. There was a hex-height Unibus board 
(jsut one obard) that was a hardware integer multiplier and divider. It 
was used with PDP11s that didn't ahve EIS (11/04, 1/05, etc) and it 
required special software support. It didn't add to the processor 
instruciton set, rahter you wrote the operands to particular I/O 
addreses and read the results back in the same way. 

I am pretty sure RT11 Fortran could use it. 


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