In my aging 2GHz Pentium 4 system I find that multiple processes are much more often contrained by disk access than by CPU availability or speed. If I launch a first and then a second big RAR decode the speed of each drops by much more than half - even though my processor is still 80% idle. Launching a third or fourth decode is totally counterproductive since they all go at a snail's pace, but again my CPU remains lightly loaded. Things are little better if I'm decoding from one drive and writing to another.
The files in question are heavily fragmented (I can't keep up with that), but I don't feel that explains the large relative changes between one and multiple decodes running.
So even while I eagerly read about the high-end quads coming up, and plan for a new PC using one, I keep thinking that high speed disks will probably be much more important to me. I should probably forego the QX9650 and settle for something lesser, putting the money saved towards ultra-fast drives (and a really good graphics card) instead.
Does anyone have similar experience with drives being so major a bottleneck in daily (non-gaming) use? To put it another way... other than certain games, where will an ultra-fast quad be significantly better than a fast quad?
One thing that should help is to get a second disc and try to run disk-intensive tasks cross-disk i.e. take a group of files from one disk and put the rar output on the other. That way you're not reading from and writing to the same disk.
I've noticed the same thing encoding/transcoding movies, the dual core helps but I'm maxing out disk usage. For games, it is going to affect your load times and some transitioning. Any faster piece = better but I think a midrange quad and some faster discs will be much better than a big fast quad.
I/o has always lagged behind processor, memory, and gpu's. The move to SATA did greatly improve I/O over IDE but it's still the slowest component in any system. Hard drives are limited by the mechanics of the head reader, platters, and spindle speeds. Solid State Drives (SSD's) will eventually change that but they will take time to become mainstream and affordable to the average consumer. You can buy a high end Alienware PC with an SSD but it adds about $400 to the price. Seagate announced a hybrid drive with 256MB flash memory to improve boot and access times. Hybrid drives seem to be a good interim step until SSD's vecome widely available.
As mentioned and in the meantime, the best way to mitigate slow disk access is to install multiple physical hard drives in your system and use them for specific tasks, i.e.; 1 drive just for the OS, 1 drive just for dl'ing and scratch work, and 1 drive just for files and storage.