COMPUTER ARCHITECTURE Lesson Note
LEARNING OBJECTIVES
This SS3 DIGITAL TECHNOLOGY lesson note covers COMPUTER ARCHITECTURE for First Term, Week 1.
Lesson Note
LEARNING OBJECTIVES
At the end of the lessons, students should be able to:
Define computer architecture.
Explain the basic components of a computer system.
Describe the Von Neumann architecture.
Explain the functions of the CPU, ALU, Control Unit and registers.
Describe the functions of the memory unit.
Differentiate between primary and secondary storage.
Explain the system bus and its major types.
Describe the fetch-decode-execute cycle.
Explain the roles of input and output units.
Differentiate between computer architecture and computer organization.
Explain different types of computer architecture.
Describe factors that affect computer performance.
LESSON ONE
MEANING OF COMPUTER ARCHITECTURE
Computer architecture refers to the design and structure of a computer system and the way its various components are organized and connected to work together.
It describes what the computer system is designed to do and how its major components interact to process data and produce information.
A computer system consists of several major components, including: Central Processing Unit (CPU), Main memory, Input devices, Output devices, Storage devices, System buses and Other supporting components
Simple representation
Input → Processing → Memory/Storage → Output
For example, when a student types 25 + 15 into a computer:
The keyboard provides the input.
The CPU processes the instruction.
The result is temporarily held in memory.
The answer 40 is displayed on the monitor.
BASIC COMPONENTS OF COMPUTER ARCHITECTURE
The major components of a computer system are:
i) Input Unit
The input unit allows data and instructions to be entered into the computer.
Examples: Keyboard, Mouse, Scanner, Microphone, Webcam and Touchscreen
Functions of the Input Unit
Accepts data from the user
Converts data into a form the computer can process.
Sends the data to the processing unit.
Allows users to communicate instructions to the computer.
ii) Central Processing Unit (CPU)
The Central Processing Unit (CPU) is the main processing component of a computer. It interprets and executes instructions and performs calculations.
The CPU is often described as the brain of the computer, although technically it is the processor responsible for executing instructions.
The major parts of the CPU include:
Arithmetic and Logic Unit (ALU)
Control Unit (CU)
Registers
ARITHMETIC AND LOGIC UNIT (ALU)
The Arithmetic and Logic Unit (ALU) is the part of the CPU responsible for performing arithmetic and logical operations.
Arithmetic operations include:
*Addition
*Subtraction
*Multiplication
*Division
Logical operations include:
*Comparing two values
*Determining whether one value is greater than another
*Determining whether values are equal
*AND, OR and NOT operations
Example
If a computer is asked to calculate:
20 + 30 = 50
The ALU performs the arithmetic operation.
CONTROL UNIT (CU)
The Control Unit (CU) controls and coordinates the activities of the computer.
It tells other components what to do and when to do it.
Functions of the Control Unit
Fetches instructions from memory.
Decodes instructions.
Controls the execution of instructions.
Coordinates the activities of the ALU, memory and other components.
Controls the movement of data between different parts of the computer.
REGISTERS
Registers are very small and very fast storage locations found inside the CPU.
They temporarily hold data, instructions and addresses that the CPU is currently working with.
Examples of CPU registers
Accumulator (ACC): Holds intermediate results of calculations.
Program Counter (PC): Holds the address of the next instruction to be executed.
Instruction Register (IR): Holds the current instruction being executed.
Memory Address Register (MAR): Holds the address of a location in memory.
Memory Data Register (MDR): Holds data being transferred to or from memory.
Registers are generally faster than RAM but have much smaller capacity.
MEMORY UNIT
Memory is the part of a computer system used to store data and instructions.
Computer memory can broadly be divided into:
Primary memory
Secondary memory
PRIMARY MEMORY
Primary memory is memory that the CPU can access directly or very quickly during processing.
Examples include: RAM, ROM and Cache memory
i) Random Access Memory (RAM)
RAM is a type of primary memory used to temporarily store programs and data currently being used by the computer. RAM is generally volatile, meaning its contents are lost when power is removed.
Importance of RAM
Allows programs to run.
Holds data currently being processed.
Helps improve multitasking.
Provides fast access to active data.
Generally, a computer with sufficient RAM can handle more active programs efficiently.
ii) Read-Only Memory (ROM)
ROM is non-volatile memory that stores important instructions needed for starting and operating a computer. Unlike RAM, ROM retains its contents when the computer is switched off.
Uses of ROM
Stores firmware.
Contains startup instructions.
Helps the computer begin the booting process.
CACHE MEMORY
Cache memory is a small, very high-speed memory located in or close to the CPU.
It stores frequently used data and instructions so that the CPU can access them quickly.
Importance of cache memory
Reduces the time required to access frequently used information.
Improves CPU performance.
Helps reduce delays between the CPU and main memory.
PRIMARY MEMORY AND SECONDARY STORAGE
Primary Memory Secondary Storage
Used directly during processing Mainly used for long-term storage
Generally, faster Usually slower than primary memory
Usually smaller in capacity Usually larger in capacity
Includes RAM and ROM include HDD, SSD, flash drives
RAM is volatile Usually non-volatile
SECONDARY STORAGE
Secondary storage is used to store data and programs for long-term use.
Examples: Hard Disk Drive (HDD), Solid-State Drive (SSD), USB flash drive, Memory card and Optical disc
Advantages of secondary storage
Stores large amounts of data.
Retains information after power is switched off.
Useful for backup.
Makes it possible to transfer data between computers.
OUTPUT UNIT
The output unit presents processed information to the user.
Examples: Monitor, Printer, Speakers, Projector, Headphones
Functions of output unit
Receives processed information.
Converts computer results into a form users can understand.
Presents text, images, sound or other forms of information.
COMPUTER ARCHITECTURE DIAGRAM
A simplified computer architecture can be represented as:
Evaluation
OBJECTIVE QUESTIONS
1. What is computer architecture primarily concerned with?
A. Designing buildings
B. The structure and operation of computer systems
C. Writing only computer games
D. Repairing electrical appliances
2. Which component of the CPU performs arithmetic and logical operations?
A. Control Unit
B. Register
C. ALU
D. Power Supply
3. Which of the following is responsible for coordinating the activities of the computer?
A. Control Unit
B. Hard Disk
C. Monitor
D. Keyboard
4. Which type of memory is generally volatile?
A. ROM
B. RAM
C. SSD
D. Flash drive
5. In the Von Neumann architecture, data and instructions are stored in ________.
A. Separate keyboards
B. The same main memory
C. The monitor
D. The printer
6. Which bus carries the actual data between computer components?
A. Address bus
B. Control bus
C. Data bus
D. Power bus
7. What is the first stage of the CPU instruction cycle?
A. Execute
B. Decode
C. Fetch
D. Print
8. Which of the following is an example of secondary storage?
A. Register
B. Cache
C. SSD
D. Control Unit
9. Which register normally holds the address of the next instruction to be executed?
A. Program Counter
B. Accumulator
C. Instruction Register
D. Memory Data Register
10. What is the main idea behind Harvard architecture?
A. It uses no memory
B. It stores data and instructions separately
C. It has no CPU
D. It uses only secondary storage
THEORY QUESTIONS
1a. What is computer architecture? Explain the major components of a computer system.
1b. Explain the functions of the following components of the CPU:
Arithmetic and Logic Unit (ALU)
Control Unit (CU)
Registers.