1.2. Computer Architecture

1.2.1. The von Neumann Architecture

1.2.2. The CPU Control Unit

1.2.3. The Arithmetic Logic Unit (ALU)

1.2.4. The von Neumann Loop

Fetch Phase

Fetch the next instruction and store it in the instruction register

Execute Phase

The ALU or I/O unit executes the instruction

• ALU does calculations
• I/O unit loads or stores data between main memory and registers

PC = <machine start address>;
IR = memory[PC];
haltFlag = CLEAR;
while(haltFlag not SET) {
    execute(IR);
    PC = PC + sizeof(INSTRUCT);
    IR = memory[PC]; // fetch phase
};