Computer Science (9618)ALU (Arithmetic Logic Unit): Performs calculations and logical comparisons Control Unit (CU): Coordinates all CPU operations, sends control signals Registers: Ultra-fast temporary storage within CPU
PC (Program Counter): Address of next instruction MAR (Memory Address Register): Address being accessed MDR (Memory Data Register): Data being read/written CIR (Current Instruction Register): Instruction being executed Accumulator (ACC): Stores ALU results
Fetch: PC → MAR → memory → MDR → CIR. PC incremented. Decode: CU interprets the opcode in CIR Execute: ALU performs operation, result stored
Topic 2 of 3Cambridge A Levels
Processor Architecture
CPU components, fetch-decode-execute cycle, and performance factors
The CPU (Central Processing Unit) is the brain of the computer. Key components:
Key registers:
Fetch-Decode-Execute cycle:
Performance factors: Clock speed (GHz), number of cores, cache size, bus width, pipelining (overlapping stages of multiple instructions).
Key Points to Remember
- 1ALU performs calculations; CU coordinates operations
- 2Registers: PC, MAR, MDR, CIR, Accumulator
- 3Fetch-Decode-Execute cycle runs continuously
- 4Performance: clock speed, cores, cache, bus width
Pakistan Example
Pakistan's IT Industry — From CPUs to Software Houses
Pakistan's growing IT sector in Lahore, Karachi, and Islamabad builds on understanding processor architecture. Software developers at companies like Systems Limited and Netsol optimise code to work efficiently with CPU resources — understanding the fetch-decode-execute cycle helps write faster programs.