Computer Architecture

Welcome, students 👋 In this lesson, you will learn how a computer is built from the inside and how its main parts work together to process data, store information, and run programs. Computer architecture is a key part of System Fundamentals because it explains the structure and operation of a computer system. By the end of this lesson, you should be able to describe the main components of a computer, explain how they interact, and use correct IB Computer Science SL terminology with confidence.

What is computer architecture?

Computer architecture is the way the hardware of a computer is designed and organized so it can perform tasks efficiently. It describes the major parts of the system and how data moves between them. In the simplest view, a computer must do three things: receive input, process data, and produce output. 🖥️

A standard computer system includes these key components:

Central Processing Unit $\left(\text{CPU}\right)$: the “brain” of the computer
Main memory $\left(\text{RAM}\right)$: stores data and instructions currently in use
Secondary storage: keeps data long-term, even when the power is off
Input devices: allow data to enter the system
Output devices: present results to the user
Buses: communication pathways that transfer data, addresses, and control signals

The CPU is often described as the part that executes instructions one after another. A program is made of instructions, and the CPU carries out those instructions using the fetch-decode-execute cycle.

Imagine a pizza shop 🍕. The customer order is the input, the kitchen is like the CPU, the ingredients in the prep area are like memory, and the finished pizza is the output. If the kitchen is organized well, the shop works quickly. If not, orders are delayed. Computer architecture works the same way: the design affects performance.

Key terms you need to know

Instruction: a command that tells the computer what to do
Address: the location of data in memory
Register: a very small, very fast storage location inside the CPU
Bus: a set of wires or pathways that carry information between components
Clock speed: the number of cycles a CPU can complete per second, measured in hertz $\left(\text{Hz}\right)$
Core: an independent processing unit inside a CPU

The CPU and the fetch-decode-execute cycle

The CPU performs most of the processing in a computer. It has several parts, especially the control unit $\left(\text{CU}\right)$ and the arithmetic logic unit $\left(\text{ALU}\right)$.

The control unit directs operations inside the CPU.
The ALU performs arithmetic operations like addition and subtraction, and logical operations like comparisons.
Registers store small amounts of data and instructions temporarily.

The CPU repeatedly follows the fetch-decode-execute cycle:

Fetch: The next instruction is taken from main memory.
Decode: The instruction is interpreted so the CPU knows what action is needed.
Execute: The CPU carries out the instruction.
Store: Results may be written back to registers or memory.

Here is a simple example. Suppose a program tells the computer to add two numbers. The CPU fetches the instruction, decodes it as an addition operation, uses the ALU to compute the answer, and stores the result. This happens extremely fast, many millions or billions of times per second.

A useful IB idea is that computer architecture affects how quickly this cycle runs. A faster clock speed means more cycles per second, but speed depends on more than just clock speed. The number of cores, the size of cache, the efficiency of instruction handling, and the type of task all matter.

For example, a video editing task may use multiple cores well, while a simple word-processing task may only need one or two. This is why a device can feel fast for one type of work but not another.

Memory, storage, and data movement

A computer uses different kinds of storage for different purposes. Main memory and secondary storage are not the same.

Main memory $\left(\text{RAM}\right)$

RAM stands for Random Access Memory. It is temporary, which means it loses its contents when the computer is turned off. RAM holds the programs and data currently being used so the CPU can access them quickly.

If you open a document and edit it, the file is loaded into RAM. This makes work fast because the CPU can reach RAM much faster than it can reach a hard drive or SSD.

Secondary storage

Secondary storage is non-volatile, which means it keeps data even when power is lost. Examples include hard disk drives $\left(\text{HDDs}\right)$, solid-state drives $\left(\text{SSDs}\right)$, USB flash drives, and memory cards.

Secondary storage is slower than RAM, but it is much larger and is used for long-term storage. A school laptop may have files saved on an SSD, but when a student opens a file, parts of it are copied into RAM for processing.

Cache memory

Cache is a small, very fast memory located close to the CPU. It stores frequently used data and instructions so the CPU can access them quickly. This reduces waiting time.

Think of cache like the items on a cashier’s counter in a shop. The most commonly used items are kept close by so the worker does not need to walk to the back storage room every time. That saves time and improves performance.

Why memory hierarchy matters

Computer architecture often uses a memory hierarchy, where faster storage is smaller and more expensive, while slower storage is larger and cheaper. A simplified hierarchy looks like this:

$$\text{Registers} \rightarrow \text{Cache} \rightarrow \text{RAM} \rightarrow \text{Secondary storage}$$

Data moves up and down this hierarchy depending on what the CPU needs. Good architecture reduces delays and helps the system run smoothly.

Buses, addresses, and system communication

The parts of a computer must communicate with each other, and they do this through buses. A bus is a pathway that transfers information between components.

There are three main types of buses:

Data bus: carries the actual data being processed
Address bus: carries the memory address of where data should be sent or fetched from
Control bus: carries control signals such as read, write, and timing signals

Suppose the CPU needs a value stored in memory. First, it places the memory address on the address bus. Then the control bus sends a read signal. Finally, the data bus brings the value back to the CPU.

This is an important concept in IB Computer Science SL because it shows that the computer is not just a collection of parts. It is a coordinated system. If the buses are too slow or too narrow, they can become bottlenecks and reduce performance.

You may also see the term word size, which refers to the number of bits a CPU can process at once. A larger word size can improve efficiency because the CPU can handle more data in a single operation.

Factors that affect computer performance

Computer performance depends on several architecture-related factors. students, it is important to remember that speed is not determined by only one feature. ⚡

Clock speed

Clock speed is the number of cycles a processor completes in one second. It is often measured in gigahertz $\left(\text{GHz}\right)$. A higher clock speed can mean faster processing, but only if other parts of the system are also efficient.

Number of cores

A multi-core CPU can handle several tasks at the same time. This is called parallel processing. For example, one core may handle a game while another core manages background tasks.

Cache size

A larger cache can reduce the number of times the CPU must wait for data from RAM. This can improve performance, especially in repeated tasks.

Bus width

A wider bus can transfer more data at once. For example, a $64$-bit data bus can move more data per cycle than a $32$-bit data bus, which may improve performance.

Memory speed and capacity

If RAM is too small, the computer may need to use secondary storage more often, which slows everything down. Good architecture balances speed, capacity, and cost.

Example comparison

A school computer used for browsing, documents, and online lessons does not need extreme processing power. A computer for 3D rendering or scientific simulations needs more cores, more RAM, and faster storage. The best architecture depends on the intended use.

How computer architecture fits into System Fundamentals

Computer architecture is one part of the larger System Fundamentals topic. System Fundamentals looks at how computer systems are designed, how they work, how data is represented, how performance is measured, and how technology affects people and society.

Computer architecture connects to these ideas in several ways:

It explains system structure by showing the role of the CPU, memory, and buses.
It supports data representation because the CPU processes binary data.
It influences performance and management because architecture affects speed, efficiency, and resource use.
It links to ethics and social impact because better hardware can reduce energy use, and waste from old hardware creates environmental concerns.

For example, a powerful server in a data center may improve access to online services, but it also uses energy and requires cooling. That means computer architecture has real-world effects beyond the machine itself.

When studying IB Computer Science SL, you should not memorize parts only as labels. You should explain how the parts work together and why the design matters. This is exactly the kind of reasoning IB asks for.

Conclusion

Computer architecture is the foundation of how computers operate. The CPU, memory, storage, and buses all work together to carry out the fetch-decode-execute cycle and run programs. Features such as clock speed, cores, cache, and bus width affect performance, but no single feature tells the whole story. Understanding computer architecture helps you explain real devices, compare systems, and connect hardware design to the broader ideas of System Fundamentals. Keep practicing the terminology and the relationships between components, students, and you will be ready to apply this knowledge in exam questions and everyday technology use. ✅

Study Notes

Computer architecture is the design and organization of computer hardware.
The main parts are the CPU, RAM, secondary storage, input devices, output devices, and buses.
The CPU contains the control unit $\left(\text{CU}\right)$, the arithmetic logic unit $\left(\text{ALU}\right)$, and registers.
The CPU follows the fetch-decode-execute cycle to run instructions.
RAM is volatile and stores data and instructions currently in use.
Secondary storage is non-volatile and keeps data when power is off.
Cache is fast memory that stores frequently used data and instructions.
The data bus, address bus, and control bus support communication between components.
Performance depends on clock speed, number of cores, cache size, bus width, and memory speed.
Computer architecture is a major part of System Fundamentals because it affects system operation, efficiency, and real-world use.