This kind of pattern shows why an SSD (Solid State Disk) makes a lot of sense. It is from Windows Performance Monitor. The top trace shows the CPU loading. As you can see the CPU is not doing that much, at best it is around half loaded. The bottom trace shows disk activity, which is pretty much maxed out.
I get this a lot, and I find it really annoying. I used to hate sitting waiting while the hard drive light flickered and my machine slowed down to treacle speed. Modern machines have addressed this issue by not having hard drive lights any more, but this isn’t really a good solution in my opinion.
A good solution is an SSD. It gives a huge improvement in the speed of the disk, particularly for reading files. Solid State Drives are also harder to break by dropping them, and they generally consume less power. I put one in my Alienware laptop and it really made a difference. I think I’m going to put one in my desktop too.
I reckon the best way to do this is to put all the system files on the SSD and then use an magnetic disk for all the documents. That way I still have space for all my oodles of files.