Introduction
Above documents provides detailed yet simple explanations of key concepts in Computer Organization, including memory management, CPU architecture, and instruction sets.
For a quick explantion of the key concepts, refer to the following details:
1. Computer Components
A computer has several important components that work together:
1.1 Input Unit
- Allows users to enter data into the computer.
- Examples: Keyboard, Mouse, Scanner.
1.2 Central Processing Unit (CPU)
- Also known as the brain of the computer.
- Performs all processing tasks.
- Has three main parts:
- Arithmetic Logic Unit (ALU): Performs calculations and logical operations.
- Memory Unit: Stores data and instructions.
- Control Unit: Manages and controls all operations.
1.3 Output Unit
- Displays processed information to the user.
- Examples: Monitor, Printer, Speakers.
2. Memory Organization
2.1 Types of Memory
- Primary Memory (RAM & ROM)
- RAM (Random Access Memory): Temporary memory, loses data when power is off.
- ROM (Read-Only Memory): Permanent memory, stores firmware.
- Cache Memory
- Small, high-speed memory between CPU and RAM.
- Stores frequently accessed data for quick retrieval.
- Virtual Memory
- Uses part of the hard disk as additional RAM when required.
2.2 Cache Memory Mapping
- Direct Mapping: Each memory block maps to a fixed cache line.
- Associative Mapping: Any memory block can be stored in any cache line.
- Set-Associative Mapping: Combines direct and associative mapping.
3. Instruction Set Architecture
3.1 Instruction Formats
- Instructions tell the CPU what to do.
- Instruction format consists of Opcode (operation code) and Operands (data or address).
3.2 Addressing Modes
- Determines how the CPU accesses operands.
- Immediate Addressing: The operand is in the instruction itself.
- Direct Addressing: The address of the operand is given directly.
- Indirect Addressing: The address field contains the address of the actual operand.
- Register Addressing: The operand is in a CPU register.
4. CPU Organization
4.1 Types of CPU Organizations
- Single Accumulator Organization: Uses one register (Accumulator) for all calculations.
- General Register Organization: Uses multiple registers for faster execution.
- Stack Organization: Uses a stack to store operands and perform operations.
4.2 Types of Instructions
- Zero Address Instructions (Stack-based operations, e.g., PUSH, POP)
- One Address Instructions (Uses one operand, e.g., ADD X)
- Two Address Instructions (Uses two operands, e.g., MOV A, B)
- Three Address Instructions (Uses three operands, e.g., ADD A, B, C)
5. Pipelining in CPU
5.1 What is Pipelining?
- A technique to improve CPU performance by executing multiple instructions in different stages simultaneously.
5.2 Stages of Pipelining
- Fetch: Get the instruction from memory.
- Decode: Understand what the instruction means.
- Execute: Perform the operation.
- Memory Access: Read or write data (if required).
- Write Back: Store the result back into a register.
6. RISC vs CISC Processors
6.1 RISC (Reduced Instruction Set Computer)
- Uses simple, fixed-size instructions.
- Executes instructions faster.
- Requires more instructions for complex tasks.
- Example: ARM processors.
6.2 CISC (Complex Instruction Set Computer)
- Uses complex, variable-size instructions.
- Fewer instructions required for complex tasks.
- Slower execution per instruction.
- Example: Intel x86 processors.
7. Input-Output Organization
7.1 I/O Methods
- Programmed I/O: CPU directly controls data transfer.
- Interrupt-Driven I/O: CPU is notified only when data is ready.
- Direct Memory Access (DMA): Transfers data without CPU involvement.
8. Memory Hierarchy
Memory is arranged in different levels based on speed and cost:
| Level | Speed | Cost | Example |
|---|---|---|---|
| Registers | Fastest | High | CPU registers |
| Cache | Very Fast | High | L1, L2, L3 Cache |
| RAM | Fast | Medium | DDR4, DDR5 RAM |
| Hard Disk | Slow | Low | HDD, SSD |
9. Summary
- The CPU is the brain of the computer, controlling all processes.
- Memory organization involves cache, RAM, ROM, and virtual memory.
- Instruction sets and addressing modes determine how the CPU processes data.
- Pipelining and CPU architectures (RISC & CISC) affect processing speed.
- I/O operations help computers interact with external devices.
- Memory hierarchy ensures efficient data storage and retrieval.
These fundamental concepts are key to understanding Computer Organization and how a computer functions at a low level.