Why is the hard drive usage so unstable?

[572]

I'm using a ordinary HDD, with normal performace.
But sometimes my HDD's data transfering speed goes very different..

Sometimes my HDD can have a high speed with 30 ~ 70 MB/s but not holding many usage,
However sometimes my HDD can only up to a low speed with 0.1 ~ 0.3 MB/s and its usage comes 100%...
(High usage will cause lag... )

 

[Tom Tancredi]

First your disk usage in the second image is 0MB/s the .1Mbps your quoting is how much it is using on NETWORK, completely different thing.
That said, if you have a 5400RPM drive, it will be SLOOOOOWWWWW and thus takes LOOOOONGER to read the data causing the visual '100% usage' as the data is read and read and read and read very..... very... slowwwwwllly as compared to what Windows 8 would like it to be (SSD). It all depends on is the program looking for a lot of different large data sets, or just a handful of small ones, all depends on the programming and such. Small data sets are going to be 'faster' to be read then a few LAAAARGEEE ones taking alot of time to 'read'.