Computers are now used in most government offices, banks and schools of Nepal, so basic computer knowledge is tested in many Lok Sewa exams. This note explains the core ideas in simple language: what a computer is, how it developed, its main parts, memory, software and the number systems it uses. Learn the tables and full forms carefully because short objective questions are often taken from them.
1. What is a computer?
A computer is an electronic machine that accepts data, processes it according to a set of instructions and gives the result as information. The instructions given to a computer are called a program.
The basic working of every computer follows the IPO cycle:
- Input: data and instructions are entered, for example by typing on a keyboard.
- Process: the computer works on the data, for example adding numbers.
- Output: the result is shown or printed.
- Storage: data and results can be saved for later use.
Raw facts and figures are called data; processed, meaningful data is called information. Important features of a computer are speed, accuracy, storage, diligence (it does not get tired) and versatility (it can do many kinds of work). A computer has no thinking power or feelings of its own; it follows instructions. If wrong data is entered, wrong results come out, which is summed up as GIGO (Garbage In, Garbage Out).
Charles Babbage is widely called the father of the computer because he designed the Analytical Engine, a mechanical machine that had the main ideas of a modern computer.
2. Generations of computers
The history of electronic computers is divided into generations according to the main technology used in their circuits.
| Generation | Main technology | Key features |
|---|---|---|
| First | Vacuum tubes | Very large, used a lot of power, produced much heat; machine language. Example: ENIAC |
| Second | Transistors | Smaller, faster and more reliable; assembly and early high-level languages |
| Third | Integrated Circuits (IC) | Many transistors on one small chip; keyboards, monitors and operating systems became common |
| Fourth | Microprocessors (VLSI) | A whole CPU on one chip; personal computers and laptops |
| Fifth | Artificial Intelligence (ULSI and parallel processing) | Aims at machines that can learn, understand natural language and make decisions |
Each new generation made computers smaller, cheaper, faster and more reliable.
3. Hardware: input, output and CPU
Hardware means the physical parts of a computer that we can touch.
Input devices send data into the computer: keyboard, mouse, scanner, microphone, webcam, joystick, light pen, barcode reader and touch screen.
Output devices give results from the computer: monitor, printer, speaker, projector and plotter. Output on screen is called soft copy, and printed output on paper is called hard copy.
The CPU (Central Processing Unit) is called the brain of the computer. It has three main parts:
- ALU (Arithmetic Logic Unit): does arithmetic work such as addition and subtraction, and logical work such as comparing two values.
- CU (Control Unit): controls and directs all parts of the computer; it fetches instructions, decodes them and tells other parts what to do. It does not process data itself.
- Registers: very small, very fast storage places inside the CPU that hold the data and instructions being used at that moment.
The main circuit board that connects the CPU, memory and other parts is called the motherboard.
4. Types of memory
Memory stores data and instructions. It is divided into primary and secondary memory.
Primary memory (main memory) is directly used by the CPU.
- RAM (Random Access Memory): read and write memory that holds the programs and data currently in use. It is volatile, which means its contents are lost when the power goes off.
- ROM (Read Only Memory): holds permanent instructions, such as the start-up program (BIOS). It is non-volatile, so its contents stay even without power. Types include PROM, EPROM and EEPROM.
Cache memory is a very fast, small memory placed between the CPU and RAM. It keeps frequently used data so the CPU does not have to wait for slower RAM.
Secondary memory (auxiliary memory) stores data permanently in large amounts. It is slower than primary memory and non-volatile. Examples: hard disk, SSD (Solid State Drive), CD, DVD, pen drive and memory card.
From fastest to slowest the usual order is: registers, cache, RAM, secondary storage.
5. Units of memory
The smallest unit of data is a bit (binary digit), which is either 0 or 1. Computers count memory in powers of 2, so each bigger unit is 1024 times the one before it (from KB upward).
| Unit | Equal to |
|---|---|
| 1 Nibble | 4 bits |
| 1 Byte | 8 bits |
| 1 Kilobyte (KB) | 1024 Bytes |
| 1 Megabyte (MB) | 1024 KB |
| 1 Gigabyte (GB) | 1024 MB |
| 1 Terabyte (TB) | 1024 GB |
One byte is usually enough to store one character, such as the letter A. Example: 2 GB = 2 × 1024 = 2048 MB.
6. Software
Software is a set of programs that tells the hardware what to do. It cannot be touched.
- System software runs and manages the computer itself. Examples: operating systems, language translators (compiler, interpreter, assembler) and device drivers.
- Application software is made to do a particular job for the user. Examples: word processors, spreadsheets, presentation programs, web browsers, accounting and payroll programs.
- Utility software helps maintain and protect the computer. Examples: antivirus, disk cleanup, disk defragmenter, file compression and backup tools.
A compiler translates the whole program at once, while an interpreter translates and runs it line by line. An assembler converts assembly language into machine language.
7. Operating system
An operating system (OS) is the most important system software. It acts as a bridge between the user and the hardware. Its main jobs are:
- managing memory, files and folders
- managing the CPU and running programs
- controlling input and output devices
- providing security through user accounts and passwords
- giving the user an interface to work with
An OS may have a CLI (Command Line Interface), where the user types commands, as in MS-DOS, or a GUI (Graphical User Interface), where the user clicks icons and menus, as in Windows. Common operating systems are Windows, Linux, macOS, Android and iOS. Linux is an example of open source software, whose source code is freely available. Starting a computer and loading the OS is called booting.
8. Number systems
| Number system | Base | Digits used |
|---|---|---|
| Binary | 2 | 0 and 1 |
| Octal | 8 | 0 to 7 |
| Decimal | 10 | 0 to 9 |
| Hexadecimal | 16 | 0 to 9 and A to F (A = 10, F = 15) |
Computers work in binary because their circuits have only two states, on and off.
Worked example: change decimal 13 into binary. Divide by 2 again and again and write the remainders.
- 13 ÷ 2 = 6, remainder 1
- 6 ÷ 2 = 3, remainder 0
- 3 ÷ 2 = 1, remainder 1
- 1 ÷ 2 = 0, remainder 1
Read the remainders from bottom to top: 13 in decimal = 1101 in binary.
Check by changing back: 1 × 8 + 1 × 4 + 0 × 2 + 1 × 1 = 8 + 4 + 0 + 1 = 13.
9. Common full forms
| Short form | Full form |
|---|---|
| CPU | Central Processing Unit |
| ALU | Arithmetic Logic Unit |
| RAM | Random Access Memory |
| ROM | Read Only Memory |
| BIOS | Basic Input Output System |
| USB | Universal Serial Bus |
| GUI | Graphical User Interface |
| OS | Operating System |
| SSD | Solid State Drive |
| VDU | Visual Display Unit |
| OCR | Optical Character Recognition |
| MICR | Magnetic Ink Character Recognition |
| ASCII | American Standard Code for Information Interchange |
| IC | Integrated Circuit |
📌 Key points to remember
- A computer accepts data, processes it and gives information (IPO cycle).
- Charles Babbage is called the father of the computer.
- Generations: vacuum tubes, transistors, ICs, microprocessors, artificial intelligence.
- CPU is the brain; it has the ALU, CU and registers.
- RAM is volatile; ROM is non-volatile and holds start-up instructions.
- Cache is a fast memory between the CPU and RAM.
- 1 byte = 8 bits; 1 KB = 1024 bytes; each larger unit is 1024 times the smaller.
- System software runs the computer; application software does user tasks; utility software maintains it.
- The OS is the bridge between user and hardware; Linux is open source.
- Binary has base 2, octal 8, decimal 10, hexadecimal 16.
- Decimal 13 = binary 1101.
Test yourself: Computer Fundamentals
24 questions check what you read about What is a computer?, Units of memory and Common full forms.