Originally posted by: Cr0nJ0b
Thanks for the response. The question about CPU versus memory was poorly worded. What I was getting at, is if I have a fast CPU but limited amount of memory, will the system be slower than if I have more memory? If I have faster memory will that have a greater effect than Faster CPU etc.
Actually, there's 2 effects here, the amount of memory application uses, this is normally fixed for a given application/wu, and as long as you've got enough memory so don't start swapping to disk, adding more memory won't help. Now Seasonal Attribution is out of work, probably the project demanding most memory is WCG's Help Defeat Cancer, that demands 716 MB and routinely uses atleast half of this. Since CPDN has been mentioned, it's using around 75 MB, meaning other projects like Rosetta@home can use more.
But, atleast for SETI@home, crunching-speed can depend on available memory, there low-end 32 MB-systems will use no caching but re-calculate everything, while systems with enough memory will use 2? different caches and re-use values for some of the calculations, and can peak-out at 100 MB used memory. Not sure on the actual memory-limits for starting to use caching, but would guess at 256 MB memory or more there won't be any benefit with adding more memory... this as long as don't start to swap that is.
So, to the 2nd. effect, and normally most important, some projects is heavily dependent on memory-speed and memory-bandwidth. AFAIK the most heavily dependent is CPDN, there increasing memory-speed can have a huge effect on speed, while increasing cpu-speed can give little benefit. SETI@home is also dependent on memory-speed, but to a lesser extent than CPDN. If you've got a dual-channel capable mainboard and a choise of same-speed 1x512 MB or 2x256 MB memory, for SETI@home and CPDN 2x256 MB is better.
Some other projects seems to be little influenced by memory-speed, and raw cpu-speed is the major contributor. Example Einstein@home and Folding@Home's Tinker/Gromacs seems to be little influenced by memory-speed...