Computer Architecture: Von Neumann Architecture

Computer Architecture

• Computer architecture is the organisation of components that make up a computer system and the operations that guide its function.

Von Neumann Architecture

• Consists of a single, shared memory for programs and data, a single bus for memory access, an arithmetic unit, and a program control unit
• Features include a central processing unit, direct access to memory, stored programs made up of instructions that can be executed in sequential order, and computer memories that can store programs as well as data

Components of CPU

Arithmetic Logic Unit (ALU)

• Carries out arithmetic and logic operations on operands in computer instruction words
• Can be divided into two units: an arithmetic unit (AU) and a logic unit (LU)

Control Unit

• Acts as the brain of the CPU, controlling and managing the execution of instructions
• Determines the sequence of operations, directs the flow of data, and ensures proper coordination among different components

Registers

• Small storage units inside the CPU that hold data, instructions, and the current status of the processor
• Essential for enabling the CPU to execute tasks quickly and efficiently

Current Instruction Register (CIR)

• Temporarily stores the instruction currently being executed by the processor
• Holds the instruction fetched from main memory

Accumulator

• A register or memory location used to store intermediate results of arithmetic and logical operations

Memory Address Register (MAR)

• Stores the memory address from which data will be fetched to the CPU registers or the address to which data will be sent and stored via system bus

Memory Data/Buffer Register (MDR)

• Holds the information fetched from main memory
• Operates as a buffer between CPU and memory

Program Counter

• Holds the address of the next instruction to be executed in memory

System Bus

Address Bus

• Carries addresses throughout the computer system between the processor and memory

Data Bus

• Carries data from processor to memory, which can be an address, instructions, or numerical value

Control Bus

• Carries signals from control bus to all other computer components
• Carries the clock's pulses

Fetch Decode Execute Cycle

• The process used by a computer's CPU to run instructions
• Each cycle retrieves an instruction from memory (fetch), translates it into a series of commands (decode), and then performs the required action (execute)

Fetch

• Retrieves the instruction from memory at the address specified by the program counter (PC)
• PC is then incremented to point to the next instruction in memory

Decode

• Splits the instruction into operand and opcode to determine what type of instruction needs to be carried out

Execute

• Performs the actual computation or manipulation of data

Memory Unit

• Primary storage/memory, also known as main memory
• Stores current data, programmes, and instructions