-First off we have platters in the drive itself. The platters are made up of ceramic and aluminum materials. The idea is to find a combination that will keep heat to a low. There is a lot of heat generated by the hard drive and it needs to keep cool, we do not want the platters expanding and contracting to much. Now along with these platters we may have as much as 1 gigabyte per platter. How is this read?
-Read/Write head moves over the disk via an actuator (arm). This head moves over grooves called tracks like a record player. Now in these track we have some more real-estate called sectors. The sector is smallest unit on the platter and its bytes are addressed within its position of the sector. Now if you can imagine all these platters on top of one another and the sectors are all lined up this is considered a cylinder. I guess because in a 3D kind of way the sector is one piece going from top to bottom. When the read/write head puts information or reads information from the drive it has to do this by scanning the sectors in a cylinder. This is pretty important when it comes time to defragment the hard drive. We want all related information close together and in a fashion that it is found fast. We will get into this more with File Allocation Table of the Hard Drive (FAT).
