What is a file organization?

It is a record store on a magnetic storage device.Magnetic disk storage is available in many forms, including floppies, hard-disks, cartridge,

exchangeable multi-platter, and fixed disks. The following deals with the concepts which are

applied, in many different ways, to all of the above methods.

A typical disk pack comprises of 6 disks held on a central spindle. As the top and bottom are

disregarded with recording information, only 10 surfaces are used, each with 200 concentric

recording tracks. A diagrammatic representation is shown in Figure 1.

Each of the 200 tracks will be capable of holding equal amounts of information as this is a feature

that is provided by the special software (housekeeping) that is used in conjunction with the handling

of disk files. When the unit is in position in the drive, the tracks are accessed by a comb of 10

read/write heads held rigidly on an arm assembly which moves in and out between the disk as

illustrated. In this way 10 tracks may be referenced without further movement of the heads once

they are positioned over the first track. For the sake of economy it is therefore usual to record over

a 'cylinder' of data (see Figure 1) and avoid unnecessary movement of the heads.

The disk pack is loaded onto the drive and revolves at normal speed of approximately 3600 rpm

when being accessed. Each track can hold upwards of 4000 bytes. Sometimes the sectors on a

disk are used in a similar manner to inter-block gaps on a tape file but in other cases they are

ignored as far as data handling is concerned.

Because this device has the ability to locate an area of data directly it is known as a Direct Access

Device and is popular for the versatility that this affords. Direct access devices provide a storage medium which is a satisfactory compromise between main store and magnetic tape.