HD Functional Units

How the hard drive is divided up

Platters are divided up into smaller units to allow for more precise accessing of data. When the system requests data from the hard drive, the hard drive knows where to go because of the specific location that is given for the data. This info should help all of you out there who are, or plan to be, "do-it-your-self" people who plans to build their own system or upgrade your hard drive. (For further do-it-yourself info, check out our Upgrade Primer). Otherwise, it's mainly a "for your information" section.

Tracks

Okay, so the platter is divided up into smaller divisions. These are called tracks, which are concentric circles on the platter. Think of this like the cross-section of an onion. Now tracks are broken down even further into sectors, which hold 512 bytes of data each. To understand what cylinders are requires a little bit more visualization. Remember how platters are stacked on a spindle? Ok now say you have 2 platters, one above the other. If you picked the same track from the top and bottom platter, a cylinder is created.

Cylinders

A cylinder is a name given to the grouping of the same track on each platter. Since the platters are stacked, if you picked the same track for each platter, you can visualize a cylinder being formed. I know this is really confusing so let me try one more time: say you take track 1 of each platter. A cylinder is formed (because the tracks are numbered the same on the platters) when you take track 1 from each platter that's stacked on the spindle.

A cylinder is not a crucial concept. The reason such a name was even created was because the read/write heads are all attached together by an actuator arm, so when one read/write head is at track 1, sector 1 of the platter 1, then the other read/write heads for the other platters are also located at track 1, sector 1 of their platters.