Disk performance is based on the speed of the disks and how busy they are. Generally disk IO isn't an issue with common web applications, although for very busy sites they can be.
If you are worried about performance and believe that it's disk related, check out Performance Monitor -> Physical Disks -> %Idle Time, Disk Queue Length, reads/sec, writes/sec, transfers/sec.
As for where the innumerable data is, it depends on what you do with it. If you filter your queries as you call them from the database then it's the database engine that does the initial work (usually best). That will use both CPU and disk IO.
If you further innumerate it from within code, then it's the CPU that will do the work.