Here's the rub. Every time the page file is accessed that's one LONG seek to that partition. You can find tomes (web pages) about this.
But the most common reasons are forgotten motherboard drivers and the old XP DMA issue. We can't count on XP to report the DMA proper so we set it to PIO, OK it and then back to DMA and OK it. Repeat for all channels.
Another common item I see today is overlapping protections. Mix Spybot's Teatimer and Norton (there are some dozen combos like that) and the machine runs hard and slow.
What confuses the usual owners is "I didn't change a thing." But we still find the usuals at play.
I'm usually pretty good at getting under the hood and solving odd problems, but this one has me bewildered.
The computer is an HP pavilion 763n. P4-2.4, 160GB primary (with second partition for pagefile) and 160GB secondary drive aliased to "My Documents." 2GB RAM, XP home sp3 updated religiously. Norton NIS also updated religiously.
About 2 weeks ago, I noticed the hard drive was audibly running virtually all the time. If I restart the computer, it runs normally for about six or seven minutes and then the HD starts running away with itself again, with NO CHANGE in the process table. Everything in the table looks completely normal. System Idle Process hovers near 99%. There's nothing unusual in "Scheduled Tasks." I disabled Windows Search. I disabled indexing. I turned Norton off. I checked manually for viruses, spyware, sevearl different ways with several different products. And the computer's speed and even HD access seem totally unaffected. This goes on and on, even when I am running no software at all. I kill all killable processes, one by one, and there's no change. Whatever is going on here, it seems totally invisible. I'm completely baffled.
And no, I've changed nothing. Installed no new software, done no reorganizing or repartitioning. (The pagefile has been in a separate partition for a couple of years now.)