Units of Masurements of Memory & Storage

Data Representation

Most of the work done by a computer can be termed as data processing. The computer is provided with data and it processes that data into meaningful information. Based on this information, further action may be initiated by the user or by the computer itself. The documents from with the data is taken and provided to the computer are called source documents . For example, the preparation of mark lists from the answer scripts of the students. Here, the answer scripts are the source documents for preparation of marks lists. Now, from these lists the report books may be prepared and for report books, these lists are the source documents. Thus, a source document may be defined as a documents from which the data is to be taken for further processing.

There are two types of data which are stored and processed by computers, namely characters and numbers. Characters include letters and symbols while numbers represent numeric values.

The characters and numbers are fed to a computer, and the output from the computer, must be in a from which is usable by people. For this purpose, natural language symbols and decimal digits are appropriate. These constitute the external data representation. On the other hand, the representation of data inside a computer musts match the technology used by the computer to store and process data. Thus, we should first determine the most appropriate internal representation of data and then specify unique transformation rules to convert external representation to internal representation and vice versa.

ASCII Code

Coding of characters has been standardized to facilitate exchange of recorded data among computers the most popular standard is known as ASCII (American Standard Code for Information Interchange). Besides codes for characters, in this standard, codes are defined to convey information such as end of line. End of page, etc. to the computer. These codes are said to be non-printable control characters.

Binary Digit = Bit
Binary Digit = Bit

• 8 bits = 1 byte
• 1024bytes = 1 kilo byte
• 1024 kilo bytes = 1 MB
• 1024 MB = 1 GB
• 1024 GB = 1 TB (Tera byte)

Data Storage

Computer is very popular due to various reasons. Among those reasons, information string ability of a computer is very important. Computer technology has the highest storing capability. Storing data in a computer is also relatively reliable. Furthermore, it is also possible to easily retrieve data stored in a computer.

Magnetic tapes

A magnetic tape is a popular medium for storage of large amount of information. These magnetic tapes are similar to the ones used in audio– cassette recorders. Apart from the use of these tapes as a storage media, these tapes also serve as high speed input and output media, A magnetic tape is made of a plastic material whose one side is coated with a magnetic substance. This substance gets magnetized easily and can retain the magnetism permanently.

Magnetic Hard Disk

Magnetic disks are smooth metal plates coated on both sides with a thin film of magnetic material. A set of such magnetic plates are fixed to a spindle one below the other to make up a disk pack.

The disk pack is mounted on a disk drive. The disk consists of a motor to rotate the disk pack about its axis at a speed of about 3600 revolutions per minute. The drive also has a set of magnetic heads mounted on arms. The arm assembly is capable of moving in and out in a radial direction

Information is recorded on the surface of a disk as it rotates about its axis. Thus, it is on circular tracks on each disk surface. A set of concentric tracks are recorded on each surface. A set of corresponding tracks in all surfaces of a disk pack is called a cylinder.

Floppy disk

The growing market for low-cost micro computer created the need of low-cost high capacity storage. This led to the development of floppy disks. Floppy disks are made of magnetic oxide- coated flexible plastic material. The flexible material is cut into circular pieces of 5.25 inches in diameter. Mini floppy drives use 3.5 inch diameter floppy disks. The floppy disk with diameter 3.5 is common in use as the material used is not a hard plate, but a flexible plastic, it is called a “floppy disk”. The flexible floppy disk is packed in a plastic envelope inside which the floppy can rotate.

Optical storage

In recent times optical techniques are also used to record data. In this category CD-ROM storage media is quiet popular. The term CD-ROM stands for compact disk read only memory. Data can be written to a CD-ROM only once. In the recent times, there are various forms of CD-ROM are in the market. For example, we can write to some CD-ROM more than once. They are called re– recordable CDs. In contrast to floppy or hard disks, a CD-ROM has one long spiral track on which data recorded ,