Understanding How Hard Disks And Diskettes Wo

DocumentID: 642876
Revision Date: 29-Feb-96 8:18:48 PM

The information in this document applies to:
WordPerfect® 5.1 for DOS

Problem

Solutions: Computers have a binary thought process. The memory of a computer consists of 0's (zeros) and 1's (ones). Information in the computer's RAM (Random-Access Memory) is stored on a memory chip as an On or Off signal. A "1" is used for the On signal and a "0" is used for the off signal. When a user creates a document, RAM stores the entire document as a series of 0's and 1's. Inside the hard disk, a motor spins a stack of flat metal disks at about 3600 revolutions per minute. Both floppy diskettes and hard disks, often called magnetic media, are coated with a magnetic oxide similar to the surface on a cassette tape. In order to store computer information on magnetic media, only two signals are needed: a strong signal and a weak signal. The computer interprets a "1" as a strong magnetic signal, and "0" as a weak signal. Thus, a pattern of 1's and 0's are written to and then read from magnetic media. When a portion of the disk is not suitable for use, it is typically called a bad sector. A computer disk is sort of a cross between a record and a cassette tape. Information on the disk is stored on magnetic tracks (like the magnetic coating on the cassette tape), and is similar to the grooves on a record (except that you cannot see the magnetic tracks). A small head, comparable to the recording head on a tape recorder, rides just above the surface of the disk. This head writes and reads magnetic signals to and from the disk in patterns of 0's and 1's. The recording head does not simply hold its position in one place; it is constantly being flicked back and forth from the outer edge in towards the hub (center) and back again, as it seeks, reads, and writes to one of the hundreds of sectors where data is stored. Tracks and sectors are better understood if you understand how disks are organized. DOS prepares information for storage, and then keeps track of the information stored on a disk. When a disk is formatted, either floppy diskette or a hard disk, circular areas called tracks are written (magnetically) on the disk. A standard 360K floppy diskette has 40 tracks, numbered 0 to 39. In contrast, a high density floppy disk (1.2M) has 80 tracks. Each track consists of a number of pieces called sectors. The top and bottom of two-sided disks contain tracks, and a pair of matching tracks on a disk is called a cylinder.

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