
Originally Posted by
Don Nelson
No, the machine doesn't "have to search through more RAM and this slows it down"...the machine knows exactly (and what address) the data/instructions exists in the memory heirarchy L1, L2, (L3 if exists particularly in server, e.g. XEON), RAM, (SSA if in system), and hard disks. It goes precisely there and is not slowed down searching through more RAM.
MORE RAM IS BETTER, and unless you are a gamer you don't need the fastest RAM, either.
Actually, having more RAM dollar-for-dollar than faster RAM will improve system performance. Here's why: If the machine finds the page resident in the RAM, it does not have to make the EXTREMELY SLOW access to hard drive to load the data (or the SLOW access to SSA if you have it in system). (and if it needs to write dirty pages out to hard drive to make room in ram, this means an even longer time). So having MORE RAM means more and more data and program instructions are found to be resident in the relatively fast RAM, and the computer runs faster as it does not have to wait for the data on the very slow disc drives (even those with cache on the drives are very very slow to the processor). Now having bigger L2 and L1 caches on the die means the machine runs even faster if the data and program is resident in L1 or L2. (If you want to study caching, LRU strategy, cache snooping algorithmes, dirty bits, performance modeling - there are excellent books available.)
Editing images means that unless you have a lot of RAM, you are going to spend a lot of time waiting for pages to be cached in and out of the hard drive.
See your PS selections on EDIT->PREFERENCES->PERFORMANCE
Notice that you are giving PHOTOSHOP a section of the RAM to manage? and that you've selected one or more discs for a scratch disk cache for editing the image.
The more RAM you have to give PS, the faster it will run. More RAM means less paging to/from the EXTEREMLY SLOW scratch disk while editing. That scratch disk is there for PS to use when it can't put everyting in RAM.
The assumption that only the fastest RAM helps means you are paying a lot for the few binned out fast parts that gamers pay a premium for. Gamers are willing to pay for fastest systems - these aren't needed for normal Photoshop image editing by most bird photographers.
Bottom line for PS users - get a new Sandybridge machine (i7-xxxx digits("second generation"; not i7-xxx), put at least 8GB of 1333 or 1600(12GB, 16GB or 24GB would be even better), use a 64 bit operating system, and you'll be fine.
And by the way, Get your RAMs now. A certain amount of SRAM capacity was in northern Japan (unlike processor production where there is ZERO Japanese production and zero Japanese assembly). And if you are building your own system, be absolutely certain to check the motherboard manufacturers information as to which of the RAMs have been tested. Not all manufacturers actually meet the specs. Not surprisingly, these are also the suppliers that generally have the cheapest prices.