Primary Memory or Primary storage (Memory)

Primary memory is also called primary storage or simply memory. It is built in within the computer.

Primary Memory :-
It is also called as main memory or internal memory. It is faster than secondary memory but it is very expensive. There are two types of primary memory:
1. RAM
2. ROM

RAM :-
RAM stands for Random Access Memory. We can read and write information in it. It is also called volatile or temporary memory because when we switch off the power supply, the whole information stored in it is erased. RAM is the working memory of the computer. All data and information must be in RAM, before processing.

ROM :-
ROM stands for Read Only Memory. The information of ROM is stored at manufacturing time but never altered afterwards. ROM is also known as Non-volatile memory because when we switch off the power supply, the information in ROM will not be erased. Basically, ROM stores the information which the computer needs all the time. The ROM basically stores computer configuration information.
The common four types of ROM are:
1. Masked ROM (Masked read only Memory)
2. PROM(Programmable Read only Memory)
3. EPROM (Erasable Programmable Memory)
4. EEPROM (Electrically Erasable Read only Memory)

Computer Types

a) On the basis of function/Activity

i) Analog computer
An analog computer is one that measures physical, continuous data such as temperature or pressure that fall along a continuous scale or variance in temperature of pressure. They give approximate result. For example an analog computer connects fuel flow measurements into quantities and price value.
Analog devices are speedometer, Seismograph, Thermometer etc.

ii) Digital Computer
The computer which accepts discrete (discontinuous) data is known as digital computer. Basically digitally computer counts digits which present numbers or letters.
Examples: IBM-PC, IBM compatibles

iii) Hybrid Computer
The data processing device, which uses both continuous and discrete data, is known as Hybrid computer.
Auto flight or Safe flight system is used in flight is known as Hybrid computer.

b) On the basis of brand / Manufacture

i) IBM-PC
The personal computer manufactured by the IBM (International Business Machine) company is known as IBM-PC.

ii) IBM-Compatible
The computers having the same functional characteristic of IBM Company are called IBM compatibles. (Assembled Computer)
iii) Apple/Macintosh
The computer developed & manufacture by Apple Company having different architecture and system known as Apple/ Macintosh computer.

c) On the basis of size / volume

i) Super Computer
Supercomputer are the most powerful and the fastest computer system, are used in weather forecasting, rocket launching, seismology, nuclear physics and so on. Examples: CRAY-1, CRAY X-MP, SX-2, HITAC S300 etc.

ii) Mainframe Computer
A Mainframe is the largest, fastest computer systems of general use having largest storage capacity; more then 100 people can work at the same time. Examples: IBM-1401, IBM-4300 HP9000model 3705/300 & 8705/400

iii) Mini Computer
Minicomputers resemble mainframe computers but they are comparatively small and less expensive.
Examples: IBM-AS/400/b60, HP-900, VAX-8842, Wipro-s68030 v, MIPS-II-52

iv) Micro Computer
A computer, which is based on microprocessor, is called a microcomputer. Types of Microcomputer are: 1. Desktop Computer 2. Laptop Computer 3. Palmtop Computer

d) On the basis of speed/model
i) XT (Extended technology) 8086, 8088 with speed 4.77 MHZ
ii) PC/AT (Personal Computer Advanced Technology) 80286, 80386, 80486. Pentium i, ii, iii, iv
iii) PS/2 (Personal System-2) other types of model from IBM since 1990.

The motherboard

The most important of any computer is the motherboard. The motherboard is the largest board of the computer system. It is also called system board. The motherboard is located on the left side of PC’s case on the bottom. It is usually green sheet of fiberglass with many chips, resisters, the heart of the computer i.e. power supply and contains many other organs of the computer system. It also contains the memory i.e. ROM and RAM and many other supporting logic circuits to make the complete work as a proper system. Instead of motherboard "IBM" refers to it as "System Board" or "Planer Board" but sometimes other manufacturer refers to it as ‘Logic Board". It accepts the CPU, memory, various plug-in peripherals, connectors and supporting circuitry. The motherboard defines the type of system by defining the type of processors it accepts, by the chipset features and by its architecture.
IBM decided that there should be used two different types of technologies, which were being used to make personal computer. They are:
Bus Based computers
Single Board Based computers
1. Bus based computers
These bus-based computers have used the main board as the backbone of the computer system. This bus board contains number of buses through which the data can be sent from one place to another and it also contains the number of slots onto which we can connect various different devices. Mainly the expansion cards are connected onto the expansion slots. In this type of bus based computer there are three buses. These are :
Address Bus
Data Bus
Control Bus
Address Bus :
Group of lines carrying the addressing information used to describe the memory location to where the data is being transferred.
Data Bus :
A set of lines used to carry the data.
Control Bus :
It is used for carrying a set of control signals that control the flow of data.
These all buses are provided on these boards. The main advantages of this type of board is that, whenever any part fails, the board on which that part is located can be removed and replaced with a working board, very easily and so it makes the maintenance of the system very easy. In these types of computers, different parts of a system such as main processor, memory, display card etc. are put on separate cards and connected to the main system bus through expansion slots.

Operating System

Operating system is the most important part of every computer system. It is collection of system programs that controls the operation of a computer system. It acts as an interface between a user and the computer hardware. The prime objective of the operating system is to manage and control the various hardware resources of a computer system. These hardware resources include processor, memory, disk space, etc. The another objective is to provide an interactive interface to the user and interpret commands so that the user can communicate with the hardware.

Functions of the operating system

The main functions of the operating system are as follows:

a) It handles allocation and de-allocation of memory space as required by various programs.

b) It manages files on a disk. It permits the users to create, print, copy, delete, read and write to files.

c) It controls input and output devices.

d) It protects system resources and information from destruction and unauthorized use.

e) It provides the interface between the user and the hardware.

Types of operating system

The operating system has evolved successfully from the primitive days to the present digital era. Several operating systems have been developed over the years. Basically, operating system is classified into two types:

a. Single-user operating system

b. Multi-user operating system

a. Single-user operating system

An operating system that allows a single user to perform just one task at a time such as printing a document, writing a file to disk, editing a file, or downloading a file from a network server is called single-user operating system. MS-DOS is the example of single-user operating system.

b. Multi-user operating system

A multi-user operating system allows multiple users to use programs that are simultaneously running on single network server. In a multi-user operating system environment, all or most of the computing is done at the server. UNIX, Linux, Novell network are the examples of multi-user operating system.

Computer Measurement Units

Memory of storage capacity measurement

We come across different measuring units like kilogram, meter and liter and so on to measure weight, length and capacity or volumes of different commodities. Similarly, when we have to measure the capacity of computer’s memory, storage devices and length of programs, units like kilogram, meter and liter can not be used. Hence, we use the units like BIT, NIBBLE, BYTE and WORD.

BIT

BIT is an abbreviation of the words binary digit and is the smallest units of information. It is either ‘0’ or ‘1’. The raw data fed into the computer are first converted into an electrical pulses or BITs, as the computer do not recognize the general form of data like numbers (0-9), alphabets (a-z or A-Z) and special characters like punctuation marks and arithmetic signs. The 0 and 1 of the binary system corresponds to the ON and OFF of the flow of electrical in the computer’s circuits. Computer works by recognizing the presence or absence of an electrical pulses or BITs at a particular time.

NIBBLE

A NIBBLE is a string of four BITs. The earliest form of code, called ‘Binary Decimal Code (BCD)’ used a NIBBLE for every character.

For example:

Character 3 A

BCD (NIBBLE) 0011 1010

BYTE

It is the unit of measuring computers memory and size of a program. One BYTE is the string of eight binary digits (BITS). It may represent a single letter, numeral or other characters. Computer memory is expressed in terms of Bytes, Kilo bytes(KB), Mega bytes(MB), Giga bytes(GB) and Tera bytes(TB).

8 bits = 1 byte

1024 bytes = 1 kilobyte (KB)

1024 kilo bytes = 1 Mega byte (MB)

1024 mega bytes = 1 Giga byte (GB)

1024 giga bytes = 1 Tera byte (TB)

A ‘Kilo’ should mean 10³ (10×10×10) that is 1000 bytes. However, since the computer used Binary system and 2¹⁰ (i.e. 2×2×2×2×2×2×2×2×2×2) equals to 1024 bytes, which is nearly 1000 bytes. Hence, ‘Kilo’ refers to 1024 in measuring units of computer.

WORD

A computer word is defined in terms of bytes. A word may be formed by combining two or more bytes. The most common combination if of four bytes. Word-length is a length of bits that occupy one location in memory. A computer having a smaller word-length is slower that another having a larger word-length is, though the speed of both is same. Word-length is generally fixed for a computer, but some computers have a challengeable word-length i.e. they can be used in doing small or big tasks. Nowadays computers have word-length of 16, 32, 48, 64, 128 or more bits.