My hard drive's a roller coaster, I just gotta ride it

[Mr Alpha]

Why does the HD Tach result for one of my hard drives look like a roller coaster?

All the other hard drives make a somewhat nice curve.

 

[imposter]

Are you sure you don't have any external programs conflicting? i remember i got this when i had a bunch of processes running in the background.

 

[CrazyIrish]

Yeah. Something else is reading/writing to the hd while hd tach is running. I get a result like that is I run two different hard drive speed tests at the same time.