The Physical Disk

Computer Engineering electronics Engineering Civil Engineering

Before file systems can be understood, the physical disk itself must also be understood. The type of physical disk that most people are used to, is a hard drive. Also known as fixed disks, they are where computers store their operating systems, program files, and data. Hard drives contain several platters, which are made up of either aluminum or more recently, glass. Glass is used in the newest and largest drives, because the platters can be made thinner, and they are more resistant to the heat that the drives generate. In order for the platters to store information, they are coated with a magnetically sensitive material, primarily containing iron oxide and cobalt alloy. The data on the platters is accessed by a head, which is moved by the head arm. There is usually one head per platter side. Figure 1 shows the primary components of a basic hard drive. Information stored on the hard drive is divided up into many distinct areas on the platters. Tracks, sectors, and cylinders are what define these areas. A track is a ring around a platter, containing information. Tracks on each platter line up with each track on the platter above or below. Each set of tracks that are identically positioned above or below each other are called cylinders. The final way that the information in hard drives is divided is into sectors. Sectors on a platter can be thought of as slices of a pie. Sectors are necessary, because there would otherwise be too much information in each track ( loading..