Re: SX cache

[roman songdog eskimo com (Bill Roman)]

Shane Steven Sturrock wrote:
> 
> [...]  We have since bought an LX from
> another company and that is proving to be 30% faster than the SX
> as expected.  Is there any physical reason why the PC164SX only
> has 1MB cache and if it had 2MB would it perform in a similar
> manner to our LX?

The difference in performance between the SX and LX is indeed due to
cache -- but there's nothing you can do about it.

The SX uses a 21164PC processor (a/k/a PCA56) rather than the 21164
(EV56) used on the LX.  One of the primary differences between the two
is that the PCA56 lacks the on-chip secondary cache of the EV56.  (It of
course still has the primary instruction and data caches on the chip.)
This causes a performance difference on the rough order of the 30%
you're seeing.

On the other hand, the PCA56 is the first Alpha chip to implement the
new Motion Video Instruction set (MVI), Alpha's answer to MMX.  These
instructions are architected (in a typically minimalist RISC style) to
speed up operations such as MPEG encoding.  Given some carefully tailored
assembly code, the SX should eclipse all other processors on such tasks.

-- 
Bill Roman  (roman@songdog.eskimo.com / roman@songdog.uucp)   running linux