That sounds also like the SuperFetch thing in Windows 7.
For those who have actually worked with your computer since the XP times, you may have once wondered what happened to certain XP computers where the behavior could only be prescribed with a comment "Foiled! The Idle process strikes again!" In this case, your computer does nothing, while looking at the task manager will show 100 % load on Idle process - it should be able to do, but it won't. Funny thing is, the Task Manager is reporting everything correctly.
I found the root cause of this from a rather informative article just a couple of months ago. In the XP machine what happened is that users were using scratched CDs that caused read errors. Now that those read errors accumulated, Windows XP decided to revert back to more robust (and slower) method of reading the CD through IDE channel, disabling SATA. The interesting part starts now: it not only affected the CD drive, but also the HDD. On top of the cake, for some boneheaded reason, Microsoft decided against letting the user know about reduction of the driver speed, leading to tens of computers prematurely retired even from the company I worked in earlier. The way to check for this is through Control Panel and checking the HDD controller whether it's operating in IDE or in SATA.
Now, you'll also encounter a similar effect with Windows 7, but the root cause is different. Some months ago I noted a curious peak in the SVCHOST process in Windows 7, when the computer started to stall for minutes. Which is really annoying when you'd like to, like, do some actual work. I downloaded an utility tool from Microsoft that allows you to open up what SVCHOST is actually doing. Included there I noticed a peak in the SuperFetch process, which is Windows predicting what the user would like to do and loading programs to RAM to make them start faster.
Again for some boneheaded reason, no possibilities were given for the users to select the programs to be loaded to RAM, and included in the loads can also be your latest .WMV that you downloaded from Netflix, totalling 4 GB. So while they are saying that the RAM access is so fast it's no problem to load stuff there and clear it for other uses, this is only a half truth. By knowing a little bit of the internals on how the computer actually works, you'll know that in order to load things to RAM, you'll have to read them from the HDD. And the way hardware is built, it only does one thing at the time, and this is specially the case for the HDD. So you are waiting for SuperFetch to load stuff from HDD that is loaded to RAM. Good luck waiting the caching of large files to RAM, only to be removed once you start a program that overwrites that memory area.
So if you are anyway serious about using your computer (expect 100 % processor loads for all cores for days and memory reservations of several gigabytes), you'll do considerably better by killing SuperFetch from the Processes. And this actually also applies up to Windows 10.