I was working on a Samsung laptop with Windows 8.1 where the machine's performance was subpar and I found that Task Manager shows disk usage was 100% (CPU and memory usage were normal). When I opened resource monitor, I didn't see any programs using any more disk than normal. Mostly from this page:
I decided to disable superfetch, which worked for me. Disk usage dropped to single digits and would rise to 100% if/when the superfetech service was re-enabled.