Computers and their components - Principal Operations

This section describes the fundamental operations performed by the key hardware components within a computer system. Understanding these operations is crucial for comprehending how a computer processes information and executes instructions.

1. The Central Processing Unit (CPU)

The CPU is the 'brain' of the computer. It fetches instructions from memory, decodes them, and executes them. This cycle is known as the fetch-decode-execute cycle.

1.1 Fetch-Decode-Execute Cycle

1. Fetch: The CPU retrieves the next instruction from main memory (RAM). The address of the next instruction is held in the Program Counter (PC).
2. Decode: The instruction is decoded to determine the operation to be performed and the operands (data) involved.
3. Execute: The instruction is carried out. This may involve performing arithmetic or logical operations, accessing memory, or controlling other components.
4. The Program Counter (PC) is incremented to point to the next instruction.

The speed at which the CPU can perform these operations is a major factor in the overall performance of the computer, often measured in Hertz (Hz) or Gigahertz (GHz).

1.2 Key Components of the CPU

Component	Description
Arithmetic Logic Unit (ALU)	Performs arithmetic (addition, subtraction, etc.) and logical (AND, OR, NOT, etc.) operations.
Control Unit (CU)	Fetches instructions, decodes them, and controls the execution of those instructions. It manages the flow of data within the CPU and to other components.
Registers	Small, high-speed storage locations within the CPU used to hold data and addresses during processing. Examples include the Program Counter (PC), Instruction Register (IR), and Accumulator.
Cache Memory	Small, fast memory used to store frequently accessed data and instructions, reducing the time it takes to retrieve information from main memory. Levels of cache (L1, L2, L3) exist, with L1 being the fastest and smallest.

2. Memory (RAM)

Random Access Memory (RAM) is the computer's primary working memory. It stores data and instructions that the CPU is actively using. Data in RAM is volatile, meaning it is lost when the power is turned off.

2.1 Types of RAM

Different types of RAM exist, each with varying speeds and characteristics:

• DRAM (Dynamic RAM): Requires periodic refreshing to retain data.
• SRAM (Static RAM): Retains data as long as power is supplied; faster and more expensive than DRAM.
• SDRAM (Synchronous DRAM): Synchronized with the system clock for faster data transfer.

2.2 Role of RAM

RAM allows the CPU to quickly access data and instructions, significantly improving the speed of program execution. The amount of RAM available affects the computer's ability to run multiple programs simultaneously and handle large datasets.

3. Storage Devices

Storage devices provide non-volatile storage for data and programs. This means the data persists even when the power is off.

3.1 Types of Storage Devices

Device	Description	Speed	Cost
Hard Disk Drive (HDD)	Uses magnetic platters to store data.	Slower	Lower
Solid State Drive (SSD)	Uses flash memory to store data.	Faster	Higher
USB Flash Drive	Portable flash memory device.	Variable	Medium
Optical Discs (CD, DVD, Blu-ray)	Store data using lasers to read and write information.	Slow	Low

4. Input and Output Devices

Input devices allow data to be entered into the computer, while output devices display or present the results of processing.

4.1 Input Devices

• Keyboard: Used for entering text and commands.
• Mouse: Used for pointing and selecting objects on the screen.
• Microphone: Used for capturing audio.
• Scanner: Used for converting physical documents and images into digital form.

4.2 Output Devices

• Monitor: Displays visual output.
• Printer: Produces hard copies of documents and images.
• Speakers: Produce audio output.

5. Bus System

The bus system is a set of electrical pathways that allow data to be transmitted between different components of the computer.

5.1 Types of Buses

Bus Type	Description	Speed
Address Bus	Carries the memory address being accessed.	-
Data Bus	Carries the actual data being transferred.	-
Control Bus	Carries control signals that coordinate the activities of different components.	-

The width of the data bus (e.g., 8-bit, 16-bit, 32-bit) determines how much data can be transferred at once, affecting the system's performance.