4.7.3 The Processor and its Components Flashcards
What is the overall meaning of this topic?
It is the internal hardware component of the computer that is responsible for executing the instructions of programs.
What components are there?
ALU, CU, Clock, Registers.
Define the ALU.
Arithmetic Logic Unit.
What is the ALU responsible for?
ALU is responsible for performing arithmetic calculations and logic operations.
e.g addition…, logical bitwise operations, comparisons of values, shifting…
Define the CU.
Control Unit.
What is the CU in charge of?
CU is in charge of organising the sequence in which program instructions are executed, followed by decoding the instructions.
CU is also responsible for directing the operations of all the other components of the processor.
What does decoding mean in the CU?
Decoding means analysing the opcode and operand of the instruction.
What are some tasks of the CU?
- Uses control signals to enable data to be read from and written to main memory.
- decodes instructions that the processor will execute to determine what needs to be done.
- organises sequence of micro-operations that need to be performed in order to carry out instruction.
- Uses control signals to determine operation the ALU will carry out.
What does the Clock do?
The Clock generates a timing signal which changes at a regular frequency. This is used to synchronise communication between the components of the processor and the rest of the computer system.
What is the clock speed measured?
It is measured in Hertz.
What are Registers?
Registers are small storage locations used to hold data temporarily. They have high read and write speeds.
What are General Registers?
General Registers are registers that can be used as storage for any data that is required by instructions during execution.
What are Dedicated/Special Registers?
They are specific registers assigned to store specific information.
Give the names of the Special Registers.
PC, CIR, SR, MAR, MDR/MBR
What is the PC and what does it do?
Program Counter.
Hols the memory address of the next instruction to be executed by the processor in the FDE cycle.
What is the CIR and what does it do?
Current Instruction Register.
Holds the current instruction that is currently being executed by the processor.
What is the SR and what does it do?
Status Register.
Contains a number of bits. Each bit within the SR acts as a flag to indicate if an error or exception has occurred or to enable or disable interrupts.
What is the MAR and what does it do?
Memory Address Register.
Temporarily stores the memory address of a memory location in main memory that the processor needs to access, or to be read from or written to.
What is the MDR/MBR and what does it do?
Memory Data Register/ Memory Buffer Register.
Temporarily stores the contents of a memory location that has been read from or data that is to be stored.
What does FDE stand for?
Fetch Decode Execute Cycle.
What happens in the Fetch stage of FDE?
Fetch - CPU fetches data and instructions from RAM then stores in registers.
1. PC has the next instruction to execute.
2. PC copied to MAR, then copied to address bus.
3. Address bus carries address to RAM.
4. Data bus carries the instruction stored in the address location to the CPU, saved in the MDR/MBR.
5. PC increments by 1.
6. MDR/MBR is copied to the CIR.
What happens in the Decode stage of FDE?
Decode - CPU works out what the instruction means.
1. CU decodes the instruction in the CIR. Splitting into opcode and operand, determining the type of instruction or if any additional data is needed for the instruction to execute.