Re: Cycles per ASM instruction

Sven Pran wrote:
(snip)

> Number of cycles per instruction was model dependent from the very first
> S/360 model, and IBM issued charts for all (?) 360 models. However
> as the 370 models were all microprogrammed such information became
> not only model dependent but also dependent on the actual data values
> operated upon. This meant that a specific machine instruction no longer
> had a characteristic operation time so that such charts became more or
> less meaningless and were no longer issued.

Even for S/360 many instructions were data dependent.  For some the
dependence was indicated in the table, for others a suitable
average was given.  It is the pipelined machines, microcoded or not,
where the timing also depends on neighbor instructions, and so it is
less reasonable to try to give them values.

-- glen