Disk formatting Magnetic disks come in various sizes and so each use different disk drives. Different computers have different ways of organizing data on disk surface – so they define their own tracks, sectors etc. Same case for disk manufacturers and causes problem for other computer users. The concept of disk formatting is used for to overcome these problems.

The concept says – before using a disk it must be prepared for use by a process called disk formatting. The read/write head lays down a magnetic pattern on the surface. The pattern allows the drive to organize and store data in the manner defined for the disk drive. A table (FAT) is maintained to locate tracks and sectors holding data. FAT created by formatting

Disk drive It contains all mechanical, electrical and electronic components for reading/writing to the actual disk. Contains the central shaft, access arms assembly and motors to rotate the disk and move access arms. Two types: With interchangeable magnetic disk: allows the loading and unloading of disks when they are needed. With fixed magnetic disk: the disks inside are permanently sealed.

Disk controller Disk drive is connected to and controlled by a disk controller. Receives commands from the OS and issues low level commands to the drive to perform read/write operations. Sometimes supports multiple disk drives

Types of magnetic disk Floppy disk: Hard disk: Individually packaged in protective plastic cases. It’s a round plastic coated with magnetic oxide. Has special liner to remove dust. Hard disk: Most common the winchester disks. Multiple platters are mounted on a single central shaft. The disks and the disk drive are sealed together in a container permanently. Container protects the disks from dust etc.

Advantages of magnetic disks Data can be accessed directly. Same disk can be shared by many users. On-line and off-line storage facility. Supports large storage capacity. Cost/per bit is low. Floppy is light weight. Portable. High data transfer. More durable.

Limitations of magnetic disks Hard to maintain security. Disk crash in one location may corrupt the entire disk data. Some are not easily portable. Cost/per bit not lower than tapes. Must be kept in a dust free environment.

Optical disk The disk is coated with a thin metal or other material that is highly reflective. Laser technology is used to read/write data. Disk has one long track, that starts from outermost point and spirals inward to the center. Suitable for reading large blocks of sequential data e.g. music. Slower random access compared to hard disk. Tracks are divided into sectors which have same length.

Cost/per bit is very low. Suitable for storing huge amount of data. Mostly used for software distribution. Access time: Is slower than hard disks. The disk has to slow down when read/write is being done near the outer region. Advantages: More reliable. Low cost/bit. Suitable for large sequential data. Portable.

Limitations: Read-only medium. Access speed slower. Require more complicated drive mechanism.