Structure and role of the processor and its components

• What is the primary function of a processor?

  To execute instructions to run programs
• What are the main components of a processor?

  Arithmetic logic unit, control unit, and registers

  
• What operations does the arithmetic logic unit (ALU) perform?

  Arithmetic and logic operations
• What types of operations are included in arithmetic operations?

  Mathematical operations like addition
• What are examples of logic operations performed by the ALU?

  AND, OR, and XOR
• What is the role of the control unit in a processor?

  To control the various components of the processor
• What is the purpose of registers in a processor?

  To hold data temporarily with high read and write speeds
• What are general purpose registers used for?

  Storage for any data required by instructions during execution
• What is the function of the program counter (PC)?

  To hold the memory address of the next instruction to be executed
• What does the current instruction register (CIR) hold?

  The instruction that is currently being executed by the processor
• What is the purpose of the memory address register (MAR)?

  To store the memory address of a memory location to be read from or written to
• What does the memory buffer register (MBR) do?

  Holds the contents of a memory location that has been read from or data to be stored
• What is the status register (SR) used for?

  To contain bits that indicate the occurrence of an interrupt
• What is the function of the system clock in a processor?

  To generate a timing signal that synchronizes communication between components
• What are the stages of the fetch-execute cycle?

  • Fetch
  • Decode
  • Execute

  
• What happens during the fetch stage of the fetch-execute cycle?

  The next instruction to execute is retrieved from main memory

  
• What is the first step in the fetch stage?

  The content of the PC is copied to the MAR
• How is the content of the MAR transferred to main memory?

  By the address bus
• What happens to the instruction after it is sent from main memory?

  It is sent to the MBR by the data bus
• What does the PC do after fetching the instruction?

  It is incremented by one
• What is the purpose of copying the content of the MBR to the CIR?

  To hold the instruction that is currently being executed
• What occurs during the decode stage of the fetch-execute cycle?

  The fetched instruction is decoded

  
• What does the control unit do during the decode stage?

  It decodes the content of the CIR
• How is the decoded instruction structured?

  It is split into two parts: opcode and operands

  
• What happens in the execute stage of the fetch-execute cycle?

  The instruction is carried out

  
• What is the first step in the execute stage?

  Any data required by the instruction that isn’t present in registers is fetched
• Where are the results of calculations stored after execution?

  In general purpose registers or main memory
• What is checked for changes between the execute and fetch stages?

  The content of the status register
• What is a processor's instruction set?

  The group of instructions that it can carry out
• Why might instructions for one processor not be compatible with another?

  Each type of processor has its own instruction set
• What are the two primary parts of machine code instructions?

  Opcode and operands

  
• What does the opcode specify?

  The type of operation to be carried out

  
• What do operands represent in machine code instructions?

  The pieces of data on which the operation is performed

  
• What is the addressing mode in machine code instructions?

  A bit assigned to specify how the operand is to be interpreted
• What is immediate addressing?

  The operand is treated as the actual value
• How does direct addressing differ from immediate addressing?

  The operand signifies a memory address
• What are the basic machine-code operations and their AQA assembly language equivalents?

  • Load: LDR Rx, <memory reference>
  • Store: STR Rx, <memory reference>
  • Add: ADD Rx, Ry, <operand>
  • Subtract: SUB Rx, Ry, <operand>
  • Move: MOV Rx, <operand>
  • Compare: CMP Rx, <operand>
  • Branch (unconditional): B <label>
  • Branch (conditional): B<condition> <label>
  • Logical AND: AND Rx, Ry, <operand>
  • Logical OR: ORR Rx, Ry, <operand>
  • Logical XOR: EOR Rx, Ry, <operand>
  • Logical NOT: MVN Rx, <operand>
  • Logical shift left: LSL Rx, Ry, <operand>
  • Logical shift right: LSR Rx, Ry, <operand>
  • Halt: HALT
• What is a logical shift operation?

  Shifting all bits in a number a specified number of positions
• What is an interrupt?

  A signal sent to the processor requesting its attention
• What are examples of hardware interrupts?

  Mouse movement or keyboard key presses