Processor Structure & Function Flashcards
What are the components that make up the CPU?
- Control Unit
- Busses
- Arithmetic Logic Unit
- Dedicated Registers
What is the control unit?
The part of the processor that co-ordinates the activity of all other components
What does the control unit do?
- Controls and co-ordinates the activities of the CPU.
- Directing the flow of data between the CPU and other devices
- Accepts the next instruction, decodes it into several steps, manages its execution and stores the resulting data back in memory or registers.
What is a bus?
A series of connectors that transfer signals between internal components.
What is the system bus?
The system bus consists of three separate busses, carrying control signals, addresses and data.
What are the three signal busses?
- Control bus
- Data Bus
- Address Bus
What bus are control signals sent along?
Control bus, between the control unit and the other components of the computer.
What are the various control signals?
- Memory Read
- Memory Write
- Bus request
- Bus grant
- Clock
What does memory read do?
Causes data from the addressed location in RAM to be placed on the data bus.
What does memory write do?
Causes data on the data bus to be written into the addressed location in RAM
What does bus request do?
Indicates that a device is requesting use of the data bus
What does bus grant do?
Indicates that the CPU has granted access to the data bus
What does clock do?
Used to synchronise operations.
What does interrupt request do?
Indicates that a device is requesting access to the CPU.
What is a unique feature of the control bus?
- The control bus is a bi-directional bus.
* Signals can be carried in both directions.
What is the purpose of the control bus?
Transmit command, timing and specific status information between system components.
What is the purpose of the data bus?
Provides a bi-directional path for moving data and instructions between system components.
What is a word?
- Memory is divided up internally into units known as words.
- A word is a fixed size group of digits, usually 16,32 or 64 bits, which is handled as a unit by the processor, different processors have different word sizes.
What is the purpose of the address bus?
Address bus transmits the memory addresses of words that are used as operands in program instructions, so data can be retrieved and sent back to the processor.
What is the purpose of the ALU?
• Performs arithmetic, logical and shift operations on data.
What are some examples of arithmetic operations?
- Add
- Subtract
- Multiply
- Divide
What are some examples of logical operations?
- AND
- OR
- NOT
- XOR
What are some examples are shift operations?
Move bits to the left or right within a register
What are registers?
Special memory cells that operate at very high speed.
What is the register for the ALU?
Accumulator
Where does the ALU store it’s data?
Accumulator
What are the the various other dedicated registers?
- Program Counter
- Current instruction register
- Memory address register
- Memory data register
What is the purpose of the program counter?
Holds the address of the next instruction to be executed. instruction is copied from the current instruction register.
What is the purpose of the current instruction register?
Holds the current instruction being executed, which is split into opcode and operand.
What is the purpose of the memory address register?
Holds the address in memory where the processor is required to fetch, or to where data is written.
What is the purpose of the memory data register?
Used to temporarily store data read from or written to memory, sometimes known as the memory buffer register.
What ist he purpose of the accumulator?
Hold immediate results of an instruction.
What is the purpose of the processor?
Carry out instructions from programs stored in memory.
What is the fetch decode execute cycle?
The sequence of operations involved in executing an instruction.
What are the stages of the fetch stage?
- Address of the next instruction is copied from the PC to the MAR.
- Instruction held at the address is copied to the MDR
- Contents of the PC are incremented
- Contents of the MDR are copied to the CIR ( Current Instruction Register ).
What are the stages of the decode stage?
- Instruction held in the CIR is decoded.
- It is then split into operand and opcode to determine the type of instruction it i, additional data if required is fetched from memory.
- It is then passed onto the accumulator.
- Instruction now in the CIR, the control unit can work out what needs to be done to carry it out.
What are the stages of the execute stage?
• Instruction is executed and the result is held in accumulator or stored in memory.
What is the opcode?
Opcode is used to determine the type of instruction and what hardware to use to execute it, the operation that is to be carried out.
What does the operand hold?
- Address of the data to be used with the operation, which is then copied to the MAR.
- The actual data to be operated on, which will be copied to the MDR.
