Data Storage In Computers

Storage of data 

The number of instructions and amount of data a computer can store in its memory is measured in bytes. A single character can be stored in one byte. 

8 bits        =   1 Byte( a bit can be either 0 or 1 )

1024 B     =   1 Kilobyte

1024 KB   =   1 Megabyte

1024 MB   =   1 Gigabytes

1024 GB   =   1 Terabyte 

A byte is a small group of bits treated as a unit. It is usually the number of bits needed to store one character. Normally a byte consists of 8 bits. 

Write Data means to move it or copy from the main store to backing store.

Read - Read data means to move it or copy from the backing store to main store. 

Stores differ in:

1.     The speed with which they can be accessed.

2.     Whether they can store data when the computer is not running.

3.     Whether data on they can be changed. 

Tow main categories of storage are

1.     Main store

2.     Backing store

Main Memory (main store)

There are two types of memory

1.     ROM (Read-Only Memory)

2.     RAM (Random Access Memory)

Memory is the name given to a group of chips inside the processing unit. Here data is held temporarily whilst processing takes place. 

Cache Memory

Cache is an area of memory that holds frequently accessed data or program instructions for the purpose of speeding a computer system’s performance. 

Read Only Memory (ROM) 

Is Memory which can be read from but not written to. ROM is permanent data and programs on it cannot be changed. It is not volatile. If ROM was volatile it would lose. Its data and it would not be possible to write it back. There are four types of ROM.

1.     PROM: Programmable Read Only Memory

2.     EPROM Erasable Programmable Read Only Memory

3.     EEPROM: Electrically Erasable Programmable Read Only Memory 

Random Access Memory (RAM) 

Is memory which can be read from or written to. RAM is temporary. It contents can be changed. It is usually volatile. 

The application of RAM

  1. As the working store of the computer- as the temporary store for the program which is running and data it is using.
  2. To store data being transferred to an from peripherals
  3. To store the contents of the screen 

Backing Store

A storage medium is the material on which the data is stored.

Eg. Magnetic tape, Floppy disk, CD ROM 

Storage Drive is the piece of equipment which rotates the storage medium and access the data on it. 

Characteristics of backing store

1.     Data is usually accessed using read/write heads. These transferred the data while the medium rotates in the drive.

2.     Access to backing store is slower than to main store.

3.     They are not –volatile. the data is stored on the medium until it is deleted. 

Magnetic Discs  

A typical Magnetic Disc has two surfaces or sides. Each surface holds data in circular tracks. Each track is divided into equal sections called sectors. 

There are two types of Magnetic Disks

1.     Floppy Disc: Is a light flexible magnetic disc.

2.     Hard Disc: Is a rigid magnetic Disc 

Compact Disc 

All types of compact disc can be read by a computer if you have the right player interfaces and software. 

A CD ROM is a compact disc normally of about 12cm in diameter. CD ROM’s of other sizes are also available.  Ex. Electronic books which are 8 cm in diameter.

Data is written to the disc using a powerful laser beam to burn patterns in the surface. The discs are exchangeable and easy to transport.

Access to data is faster than floppy discs but slower than hard discs.  

Multi-media means presentation on a computer of information combining animated and still graphics, sound and text.

Data Files

Facts about Files

The term File is used to describe any data or program stored on a backing store such as a disc or a tape. 

A data file is an organized collection of data. It usually consists of a number of separate parts called records. 

A Record is a subdivision of a file. It consists of a set of items of data which together can be treated as a unit. 

Storage of Files

Creating a file

Organizing data into a file means creating a file.

Saving a file

Copying all record from main store on to a backing store

Types of file