What is a computer system?
A computer system is hardware and software that work together to do a job. Hardware is the parts you can touch. Software is the instructions that tell the parts what to do.
The five main hardware jobs are: input (keyboard, mouse, camera), processing (the processor or CPU, which does the calculations), memory (RAM, a quick temporary desk for work in progress), storage (disk or SSD, a cupboard that keeps files when power is off) and output (screen, speaker, printer).
Data goes in, is processed, is kept, and comes out as a result. A computer, a phone and an ATM all follow this path.
Analysing the need
Analysis means finding out what the system must do before you choose anything. Ask four questions. Who will use it? What work will it do? How fast must it be? How much money is there?
The answers become requirements, for example: "edit 10-minute school videos without hanging" or "type letters and browse the web". Write them down in numbers where you can. A heavy job such as video editing needs a stronger processor, more memory and more storage than a typing job.
Good analysis stops two mistakes: buying too little (the job fails) and buying too much (money wasted).
Designing the system
Design means choosing parts and software that meet the requirements within the budget. You choose a processor, memory size, storage type and size, screen and any extra devices, and the operating system and programs.
You must also make the parts fit together. The processor must suit the main board, and the power supply must give enough power. Draw a simple block diagram first: boxes for each part and arrows for how data moves. Then write a parts list with prices.
Design is a trade-off. A faster part costs more. The aim is the cheapest design that still meets every requirement.
Evaluating the system
Evaluation means testing the finished system against the requirements. Run the real job, such as a sample video, and measure: how long it takes (speed), whether it hangs or crashes (reliability), how easy it is to use, how much it costs, and how much power it uses.
Compare each result with the requirement. If one part is below its target, it is the bottleneck: the weak spot that limits the whole system, like a narrow door that slows a crowd. Fixing a part that is not the bottleneck does not help.
After finding it, improve that part and test again. Real projects repeat analyse, design, evaluate, improve many times.
Try it: find the bottleneck
In the 3D, choose the job "Video edit". Set processor 5, memory 1, storage 5. The system is slow. Which bar is red? Raise only that slider to 3. Now the speed jumps. Then try raising the processor even more: nothing changes. Only the weak part matters.
At home: open Task Manager (Windows) or Activity Monitor (Mac) while a big app runs, and see which part, processor, memory or disk, is nearly full.
Key formulas and definitions
- System = hardware + software + people
- Data path: input → process → memory/storage → output
- Speed of system ≈ speed of the weakest part (bottleneck)
- Speed score % = (lowest level ÷ needed level) × 100, capped at 100%
- Total cost = sum of the cost of all parts
Worked examples
1. A job needs processor 4, memory 3, storage 3. A design has 4, 2, 3. Which part is the bottleneck?
Compare each part with its need: processor 4 of 4 (fine), memory 2 of 3 (short), storage 3 of 3 (fine). Memory is the bottleneck.
2. In that design, find the speed score. Then say what happens when memory becomes 3.
Speed score = lowest level ÷ need = 2 ÷ 3 = 0.67, so 67%. With memory 3, all parts meet the need, so the score is 100%.
3. Each level of a part costs 10 units. The design 4, 2, 3 is changed to 4, 3, 3. How much does the cost change?
Old cost = (4+2+3) × 10 = 90. New cost = (4+3+3) × 10 = 100. It rises by 10 units, which is cheap for a big speed gain.
4. Put these in order: test the system, find what the user needs, choose parts, fix the weak part.
Find what the user needs (analyse) → choose parts (design) → test the system (evaluate) → fix the weak part (improve).
5. A shop sells a PC with processor 5, memory 5 and storage 1 for a typing job that needs 2, 2, 2. Evaluate it.
Storage 1 is below the need 2, so speed score = 1 ÷ 2 = 50%. The processor and memory are more than needed, so money was wasted there. A better design is 2, 2, 2.
6. A design has levels 3, 3, 3 and the job needs 5, 4, 2. Find the speed score and the bottleneck.
Ratios: processor 3÷5 = 0.6, memory 3÷4 = 0.75, storage 3÷2 = 1.5 (capped at 1). The lowest is 0.6, so the score is 60% and the processor is the bottleneck.
Common mistakes
- Buying the most expensive processor and ignoring memory and storage. The weakest part sets the speed.
- Skipping analysis and choosing parts first. You cannot judge a design without knowing the need.
- Thinking evaluation means only looking at the price. Test speed, reliability, ease of use and cost together.
- Upgrading a part that is not the bottleneck. It costs money and the system stays just as slow.