2.1.1 CPU and Machine Instruction Cycle Notes

CPU Architecture

The central processing unit (CPU) is the brain of a computer, responsible for executing instructions and processing data. It consists of several key components, each with a specific role:

1. Arithmetic Logic Unit (ALU): Performs arithmetic and logical operations.
2. Control Unit (CU): Manages the execution of instructions by directing the flow of data within the CPU.
3. Registers: Small, fast storage locations within the CPU, including the Memory Address Register (MAR) and Memory Data Register (MDR).
4. Buses: CPU connections to primary memory and other components.

A block diagram of the CPU illustrates the relationships between its components:

The Arithmetic Logic Unit (ALU)

The Arithmetic Logic Unit (ALU) is responsible for performing all arithmetic and logical operations. It is the computational engine of the CPU, handling tasks such as:

1. Addition, subtraction, multiplication, and division
2. Logical operations like AND, OR, and NOT
3. Comparison operations such as greater than, less than, and equal to

The Control Unit (CU)

The Control Unit (CU) is the orchestrator of the CPU, responsible for:

1. Fetching instructions from primary memory
2. Decoding instructions to determine the required operations
3. Executing instructions by coordinating the ALU and other components

Registers: MAR and MDR

They play a crucial role in the execution of instructions. Two important registers are:

1. Memory Address Register (MAR):
   1. Holds the memory address of the data to be accessed.
   2. Communicates with primary memory via the Memory Address Bus.
2. Memory Data Register (MDR):
   1. Holds the data to be transferred to or from memory.
   2. Communicates with primary memory via the Data Bus.

Buses