Basic operations of a computer
A computer accepts data, processes it under program control, and gives out information, storing both for later use.
The information processing cycle (IPOS)
- back to Input
Every computer job, from a supermarket bill to a payroll run, follows these four operations.
From data to decisions
Each bill at a supermarket till is data. The daily sales report is information. Knowing that sugar and oil sell faster before the Sinhala and Tamil New Year is knowledge. Ordering extra stock is the decision.
Parts of a computer system
| Part | What it does | Simple example |
|---|---|---|
| Control unit (CU) | Fetches each instruction, decodes it and directs the other parts | A supervisor giving orders |
| Arithmetic logic unit (ALU) | Does arithmetic (+, −, ×, ÷) and logic (comparing: >, <, =) | Adding up a bill |
| Registers | Tiny, very fast stores inside the CPU for the item being worked on | The number being added now |
| RAM (main memory) | Holds the programs and data in use; cleared when power goes off | An open Excel file |
| ROM | Permanent instructions that cannot easily be changed | Start-up (boot) instructions |
| Secondary storage | Keeps data permanently, even without power | Hard disk, SSD, pen drive |
The machine cycle
The CPU repeats these four steps for every instruction, billions of times a second.
- 1Fetch: get the next instruction from main memoryControl unit
- 2Decode: work out what the instruction meansControl unit
- 3★Execute: carry out the calculation or comparisonALU
- 4Store: write the result to a register or memoryRegisters / RAM
★ one-way, controls the pace
Why businesses use computers
- Speed: millions of calculations in a second.
- Accuracy: no tiredness errors, if the input is correct.
- Storage: huge amounts of data in a small space.
- Diligence: the same job repeated without boredom.
- Versatility: one machine for accounts, letters, email and design.
- Limit: no judgement of its own. Garbage in, garbage out (GIGO).
A supermarket till in Sri Lanka shows all four operations: the barcode scanner inputs the item code, the CPU looks up the price and adds the bill, the receipt printer outputs it, and the sale is stored for stock and sales reports.
Short answer: “Distinguish between data and information.” Data are raw, unprocessed facts, such as single sales. Information is processed data that is meaningful and useful, such as a monthly sales report.
Structured question: “State the functions of the control unit and the arithmetic logic unit.” The CU fetches and decodes instructions and directs the other parts. The ALU does calculations and comparisons. Add one example of each.
Essay: “Explain the basic operations of a computer with the help of a diagram.” Draw the IPOS cycle, explain input, processing (CPU parts, machine cycle), output and storage, and give a business example.
IPOS: Input, Process, Output, Storage. Inside the CPU, the CU is the commander and the ALU is the calculator.