Quick summary
A computer (संगणक) is an electronic machine. It takes data, processes it according to instructions, shows the result and stores information. Every computer has two sides: hardware and software. This chapter covers the parts of a computer, memory and its units, and the types of computers.
Key points
- A computer does not think on its own. It only follows instructions.
- It works in four steps: Input → Process → Output → Storage.
- A computer has no IQ (no intelligence of its own).
- CPU means Central Processing Unit. It is the "brain" of the computer.
- The CPU has three parts: ALU, CU and registers.
- The motherboard is the main circuit board that connects all parts.
- The SMPS changes the AC mains supply into the low-voltage DC power the computer needs.
- RAM is temporary memory. Its data is lost when power goes off.
- ROM is permanent memory. Its data stays even without power.
- 1 byte = 8 bits, and 1 KB = 1024 bytes.
Characteristics of a computer
- Speed: does millions of calculations in seconds.
- Accuracy: gives correct results when the data and instructions are correct. Most errors come from wrong input by humans.
- Storage: can store a huge amount of data.
- Diligence: never gets tired or bored; works for hours with the same quality.
- Versatility: typing, accounts, pictures, music, internet – it does many kinds of work.
- Limit: a computer has no feelings and no intelligence of its own.
CPU, motherboard and memory
| Part | Job |
|---|---|
| ALU (Arithmetic Logic Unit) | Does calculations like addition and subtraction, and comparisons (greater/smaller/equal) |
| CU (Control Unit) | Controls and coordinates the work of all parts |
| Registers | Very small, very fast memory inside the CPU |
| Cache memory | Fast memory between the CPU and RAM; keeps often-used data |
| RAM | Holds running programs and data for now (volatile) |
| ROM | Holds permanent start-up programs (non-volatile) |
Units of memory
| Unit | Size |
|---|---|
| Bit | 0 or 1 – the smallest unit |
| Nibble | 4 bits |
| Byte | 8 bits |
| Kilobyte (KB) | 1024 bytes |
| Megabyte (MB) | 1024 KB |
| Gigabyte (GB) | 1024 MB |
| Terabyte (TB) | 1024 GB |
Software and types of computers
- Hardware: the parts you can touch – monitor, keyboard, mouse, CPU.
- Software: a set of instructions (programs) that tells the computer what to do. You cannot touch it.
- System software: runs the computer itself, for example Windows.
- Application software: does a particular job, for example MS Word, MS Excel, a web browser.
- By size: micro (personal computers), mini, mainframe (banks, big companies) and supercomputer (weather forecasting, research). A supercomputer is the fastest.
- In daily life: desktop, laptop, tablet, smartphone and server (a computer that serves other computers on a network).
Starting and shutting down
- Switch on the power supply, then press the CPU power button, then switch on the monitor.
- When work is done, save all files and close the programs.
- Click Start → Power → Shut down.
- Never just switch off the mains – data can get damaged.
Important terms
- Data – raw facts that are not yet processed.
- Information – useful result you get after processing data.
- CPU – Central Processing Unit, the brain of the computer.
- Volatile memory – memory that loses its data when power goes off (RAM).
- Booting – the process of a computer starting up.
- SMPS – Switch Mode Power Supply.
Practice questions (with answers)
Q1. Which part is called the "brain" of the computer?
- (A) Monitor
- (B) Keyboard
- (C) CPU
- (D) Mouse
Answer: (C) CPU – it does all processing and control.
Q2. How many bits make 1 byte?
- (A) 8
- (B) 4
- (C) 16
- (D) 1024
Answer: (A) 8 – 4 bits make a nibble.
Q3. Which memory loses its data when the power goes off?
- (A) ROM
- (B) Hard disk
- (C) Pen drive
- (D) RAM
Answer: (D) RAM – it is volatile memory.
Q4. Which part of the CPU does addition, subtraction and comparison?
- (A) CU
- (B) ALU
- (C) SMPS
- (D) ROM
Answer: (B) ALU – the Arithmetic Logic Unit does calculations and comparisons.
Q5. Which of these is system software?
- (A) MS Word
- (B) MS Excel
- (C) Windows
- (D) MS PowerPoint
Answer: (C) Windows – it is an operating system; the others are application software.
Exam tip
Learn the order of memory units (Bit → Nibble → Byte → KB → MB → GB → TB) and the difference between RAM and ROM – a question on these comes almost every time.