Western Digital:
Velociraptor: 10k/15k drives. Generaly low storage. 3.5" only.
Caviar: 5400/7200 drives. Normal drives from 320 to 3000gb. 3.5" only.
(Green = power efficient, Blue = normal, Black = performance)
Scorpio: 5400/7200 drives. Laptop drives. 120 to 1000gb. 2.5" only.
Note: It is extremely rare for any prebuilt desktop to come with a Caviar Black HDD, let alone a Velociraptor. In fact, 90% of the time, they come with Caviar Green drives. Same applied to laptops, only substitute Caviar with Scorpio.
If you're going to get an HDD, get it from bestbuy. They're much cheaper 'cause they have HDDs in storage because who the hell goes to bestbuy to buy an HDD, right?
And no, using CCleaner does not hold a HDD together... CCleaner wipes data off an HDD, which is causing the HDD to do work. If there is a hardware problem, nothing can help it besides getting a new HDD or possibly a new controler board for the existing one, which requires that you buy an exact match of your existing drive.