A Guide to Internal Memory in Computer

It is also called primary, core or main memory, is used to store data program (instructions set) needed for current processing. Also, after processing a particular job, the resulting output or intermediate output is retained in the memory for further processing if need be, before it is permanently stored in the external storage.

Internal memory is referred to as core memory because earlier component made use of core materials such as ferrite core as their memory. Currently, semi-conductors are used, such as silicon chips.

The internal or main memory can be categorized into two types of semi-conductor, namely:

Random Access Memory (RAM) - being volatile (Dynamic memory) which lose its formation immediately power is switched off:

Read Only Memory (ROM) - the non-volatile or static memory, which retain information when power is switched off.

Random Access Memory

When an instruction set (or program) is typed into a computer, they are put into the main memory. This program is stored in a part of this main memory called the RAM.

When the computer is switched off, this program will be lost or it will disappear from the RAM. To safe guide this; it is essential to make copy of the program on an external storage device (e.g. floppy disk, tape etc.) before switching off the computer. So, when next the computer is switched on, the program can be copied back into the RAM from the external device where it was earlier stored (before the switch off).

Read Only Memory

The ROM is the second type of main memory. It cannot be used to stored dynamic programs like the RAM. Its main function is to store some preset instructions, to tell the computer what to do. The instructions are permanent and non-volatile, programmed on the ROM chips by the manufacturer. The user of the computer system cannot change these instructions. The ROM is also called the firmware or pre-wired memory. The functions of ROM are stated below thus:

Tell the computer what to do when power in turned on

Check to see that the cable to the printer is connected

Interpret each key on the Keyboard to the control unit

There are three types of ROM chips which can be used by the user of the computer whenever the need arise. These are:

PROM - meaning Programmable Read Only Memory. It is a type of ROM that can be customized for the user. Once changed, it becomes permanent and can no longer be altered. It gives the user the flexibility to meet special needs.

EPROM - meaning Erasable Programmable Read Only Memory. This chip is erasable and re-useable. To erase the chip, it must be removed from the computer and treated through certain processes before it can be re-used.

EEPROM - meaning Electronically Erasable Programmable Read Only Memory. This allows change on the ROM chip through the use of dedicated or specialized software without removing the chip from the computer.

Eternal (Auxiliary) Storage

The external (or secondary) storage is an additional memory, used to hold data on a long-term basis. It holds large amounts of information outside the main memory. It is separate from the central processing unit and is contained in another box. A computer need not have an auxiliary storage although almost all do; a computer is more useful if it has additional external memory.

The most common type of secondary storage devices is magnetic tape, magnetic disk, etc

Floppy Disk - is usually found in microcomputers. It is a plastic disk in the shape of a circle. Information is stored on the two surfaces of the disk. To protect the surface of the disk, it is sealed inside a jacket, which is square shaped. To read or write to the disk, it is inserted in the disk dive, which is connected to the processor of the microcomputer. Two common sizes of the floppy disk are 31/2-inch version and 51/4 inch size. This floppy disk comes in two-density form: low density and high density. For the 31/2-inch size of low-density form, it can store 720-kilo byte or 720,000 characters while the high-density type can store 1.44 MB or 1.44 million characters. For the 51/4-inch size low-density disk, it can store up to 1.2 MB or 1.2 million characters.

Hard Disk - Most microcomputer today house a hard disk inside the computer boxes. It stores more characters than the floppy disk. The storage capacity of the hard disk ranges for 10 MB to Gigabytes. ON most microcomputer, the hard disk is regarded as the "C" drive while the floppy disk is tagged "A" or "B" drive.

Input Devices

Input devices are used to get data into the computer. There are various types of input devices, among which are: Keyboard, Mouse, Voice input, Visual display unit and Document Readers.

Keyboard - This is the mo common and standard input device. The keyboard is similar to the keyboard of a typewriter, but contain additional keys, which are used to control and edit the display. On the keyboard, the following can be found:

Control Key e.g. Shift Key (Shift), Alternate Key (ALT), Enter or Return Key, etc.

Function Keys - each function key as a meaning in each program or software in which it is used e.g. F1 to F12

Mouse- it is a simple device that is moved over a pad on the desk by the hand. IT moves a pointer around the computer screen and enables some commands to be sent to the computer screen. It is software dependent, that is, to use it, its driver (software) must be installed on the computer.

Voice Input Devices - This accept speech as input into the system. The hindrance in this form of input is that it is sonly capable of recognizing a few words. It also has problem in the way words are pronounced from one person to another. It is expected to be an eventual breakthrough by the time these problems are eliminated.

Visual Display Unit - It is dual-purpose device, that is, it can be used for input as well as output. A typical full screen, display 24 by 80 characters, that is, 1920 characters per screen. It display inputs made through the keyboard and allow for the detection of any error in the input, thus, allow correction to be made before permanent storage.