Title: Computer Science / Section 1: Components of a computer / Chapter 1: Processor Components

Q: What does the CU do?
A: - Directs operations within the CPU
- Decodes instructions from Memory ("LDA 5" --> "LDA" "5")
- Controls the movement of data within CPU

Q: What does the ALU do?
A: - Perfoms Arithmatic (addition, subtraction)
- Performs Logical comparisons (AND, OR, NOT)

Q: List some registers in the CPU
A: PC - Program Counter
ACC - Accumulator
MAR - Memory Address Register
MDR - Memory Data Register
CIR - Current Instruction Register

Q: What do the CPU registers do?
PC
ACC
MDR
MAR
CIR
A: PC - Holds memory address for next instruction to be fetched
ACC - Holds the result of the AUR
MDR - Stoes data being read/written to memory
MAR - Stores the address that will be read/written to
CIR - Stores current instructions that will be decoded and recievices decodes instruction from the CU

Q: Name some buses and their functions
A: Data Bus - Transports actual data between CPU, Memory and Peripherals and trasfers data from MDR to memory
Address Bus - Carries the memory address from MAR to where data is written to/read from
Control Bus - Sends control signals between CPU and hardware e.g. read from/write to memory

Q: What happens in the Fetch stage?
A: - The address (of the next instruction) is copied from the PC to the MAR
- The instruction held at the address now in the MAR is copied into the MDR
- PC increments
- Contents of MDR are copied to the CIR

Q: What happens in the Decode stage?
A: - CU decodes the instruction stored in CIR so opcode is seperate to the operand ("LDA 5" --> "LDA" and "5")

Q: What happens during the execute stage?
A: - The appropriate opcode is performed on the operand