Mechanism of a Hard Disk

In a disk drive a floppy diskette rotates at speeds of 300-400 RPM(revolutions per minute). Typically, hard disks rotate 7200 RMP. In a disk pack, all disks rotate at the same time, although only one disk is being read or written on at any one time. In the same way,  the high-density 3 1/2 inch floppy disk can  store 1.44 MB of data. Today, hard disks with the capacity range of giga-bytes (GB) are very common. With a hard disk, most people can store all their programs and files in one location. Still hard disk do not eliminate the need for a floppy disk drive. It serves as a transfer device to get software, purchased on floppies, in to hard disk. Some hard disk mechanisms for large system use moving head. in this design, all the read/write heads in a stack of disks are attached to a single access mechanism that moves directly to a specific address. This method is relatively slow, because all the access arms must move together.

A faster technology is that of fixed-head disks. These devices have fixed access arms with separate disk, read/write mechanisms for each track of the disks. The disk, rather than the head, whirls to bring the correct sector to the arm; the read/write mechanism for the depending on the application. Other disk devices combine the technologies of both moving  and fixed head access to produce a high capacity, rapid access device. With a brand new hard disk, the computer will try to place the data in clusters that are contiguous-that, is that are adjacent(next to one another). Thus, data world be stored on track 1 in sectors 1,2,3,4 and so on However as data files are updated and the disk fills up, the operating system stores data in whatever free space is available. Thus files become fragmented. Fragmentation means that a data file becomes spread out across the hard disk in many non-contiguous clusters.