1.2 Computer systems  (Page 4/8)

Hard Disk: is made of magnetic material. Magnetic disks used in computer are made on the same principle. It rotates with very high speed inside the computer drive. Data is stored on both the surface of the disk. Magnetic disks are most popular for direct access storage device. Each disk consists of a number of invisible concentric circles called tracks. Information is recorded on tracks of a disk surface in the form of tiny magnetic spots. The presence of a magnetic spot represents one bit and its absence represents zero bit. The information stored in a disk can be read many times without affecting the stored data. So the reading operation is non-destructive. But if you want to write a new data, then the existing data is erased from the disk and new data is recorded. The capacity of a hard disk is possibly 20 GB, 30 GB, 40 GB, 60 GB or more.

Floppy Disk: It is similar to magnetic disk discussed above. They are 5.25 inch or 3.5 inch in diameter. They come in single or double density and recorded on one or both surface of the diskette. The capacity of a 5.25-inch floppy is 1.2 mega bytes whereas for 3.5 inch floppy it is 1.44 mega bytes. The floppy is a low cost device particularly suitable for personal computer system.

Optical Disk:With every new application and software (includes sounds, images and videos) there is greater demand for memory capacity. It is the necessity to store large volume of data that has led to the development of optical disk storage medium. There are two commonly used categories of optical disks: CD with the approximate capacity of 700MB and DVD with the approximate capacity of 4.7GB

Memory Stick (Flash card, flash drive) a removable flash memory card format, with 128MB, 256 MB, 512 MB, 1 GB, 2 GB , 4 GB or more capacities

Input-output devices

A computer is only useful when it is able to communicate with the external environment. When you work with the computer you feed your data and instructions through some devices to the computer. These devices are called Input devices. Similarly the computer after processing, gives output through other devices called output devices.

Common input and output devices are: Speakers, Mouse, Scanner, Printer,Joystick, CD-ROM, Keyboard, Microphone, DVD, Floppy drive, Hard drive, Magnetic tape, and Monitor. Some devices are capable of both input and output.

Input Devices

Input devices are necessary to convert our information or data in to a form which can be understood by the computer. A good input device should provide timely, accurate and useful data to the main memory of the computer for processing followings are the most useful input devices.

Keyboard: - This is the standard input device attached to all computers. The layout of keyboard is just like the traditional typewriter. It also contains some extra command keys and function keys. It contains a total of 101 to 104 keys. You must press correct combination of keys to input data. The computer can recognize the electrical signals corresponding to the correct key combination and processing is done accordingly.