Re: architectural goals, Byte Addressability And Beyond

According to Lawrence D'Oliveiro  <ldo@nz.invalid>:

On Wed, 29 May 2024 07:04:35 GMT, Anton Ertl wrote:
>

Lawrence D'Oliveiro <ldo@nz.invalid> writes:
>

Isn’t the point of RISC that these complex operations are
more efficiently performed by a sequence of simpler instructions?

 
The IBM z series are not RISCs.

>
Doesn’t matter. The principles of designing high-performance architectures
still apply: simpler instructions are better than more complex ones.

Nobody buys a mainframe just for its compute speed.

I do not entirely understand why IBM keeps adding special purpose
instructions to z. Maybe it's partly marketing, but they have a
largely captive audience so it has to be more than that. Given the
millicode design, a lot of the instructions are basically microcoded
subroutines that may well run faster than the normal code equivalent
because the have access to more machine state. If anyone is about to
say than let all the instructions see all the state, see our
discussion a week or two ago about architecture vs. implementation.

If you want something that gives you more MIPS/$, IBM is happy to sell
you POWER systems.

--
Regards,
John Levine, johnl@taugh.com, Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. https://jl.ly