Hmmmm.....
Hard Drives store files.
CPU is the power that drives programs.
RAM stores programs that are running.
Bandwidth is how fast you can transfer files between servers.
You may not be noticing a difference if you're relatively new because most programs don't take up much hard drive space at all until they are upgraded quite a bit, with a few exceptions, such as the Robber Baron.
Click on "Software Types" on the left hand column of your window. You'll see data such as this:
File Share Virus Uses the host bandwidth and some CPU for sharing files and generating income. Has to be collected on the host. 250 10000 50 3276800000
CPU - Amount of CPU used while running. (In this case 250 MHz)
Memory - Amount of RAM used while running. (In this case 10,000 kb or approximately 10 Mb.)
Bandwidth - Amount of Bandwidth used while running. (In this case 50 kbs.)
Size bytes - Amount of space taken up on Hard Drive. (In this case 3 Gb.)
A little clearer?