MAX Systems
PMJI John, but I have just been reading an article concerning multiple
processors, the article itself goes on at some length about the pros and cons
of such systems and can be found in the September 1995 issue of Windows
Magazine.
Essentialy however it says the following, the apparent power gains from
multiple processors are dependant on the number of threads that the software is
using and the efficincy of the scaling factor of the CPU. Basicaly this
translates as the following: a good CPU may have a scaling factor of 0.95 thus
if we have 2 threads running on 2 CPU's with a scaling factor of 0.95 you will
get a percived speed of 2^0.95 or around 1.93 times the speed of 1 CPU, as you
increase the nuber of CPU's the scaling factor quickly becomes noticeable thus
4 CPU's gives 3.73 times the speed and 8 gives 7.2 and so on. Even this is
incorrect because the scaling factor is dependant on the number of threads, as
you run more CPU's the scaling factor decreases rapidly, because it gets harder
to avoid contention for resources between threads, also synchronisation
problems are not limited to software. I have no intention of writing out the
whole article but the above basically somes it up.
This will apply to any CPU, its just that some systems will run more
efficiantly and are better designed for multiple processors i.e. the Alpha and
possibly Intels new P6.
The conclusions I would draw are that its not worth having more than 4 CPU's
per machine, better to have more machines to do the task, It probably is for
the best anyway and is certainly just as economical.
In closing I would like to point out one additional factor multiple processors
were designed for file servers not individual apps bear that in mind before
buying machines with rediculous numbers of processors in !………
David