Components of a Computer Flashcards
Arithmetic Logic Unit
The ALU (Arithmetic and Logic Unit) completes all of the arithmetical and logical operations.
Arithmetical operations include all mathematical operations such as addition and subtraction on fixed or floating point numbers.
Logical operations include Boolean logic operations such as AND, OR, NOT, and XOR.
Control Unit
The Control Unit is the component of the processor which directs the operations of the CPU.
I has the following jobs:
- Controlling and coordinating the activities of the CPU
- Managing the flow of data between the CPU and other devices
- Accepting the next instruction
- Decoding instructions
- Storing the resulting data back in memory
Registers
Registers are small memory cells that operate at a very high speeds and are used to hold data temporarily.
Program Counter
Holds the address of the next instruction to
be executed.
Memory Address register (MAR)
Holds the address of a location that is to be
read from or written to.
Memory Data register (MDR)
Temporarily stores data that has been read or data that needs to be written.
Current instruction register
Holds the current instruction being executed, divided up into operand and opcode.
Accumulator
stores the result of calculations made by the ALU
Interrupt register
generates and detects interrupts
Buses
Buses are a set of parallel wires which connect two or more components inside the CPU.
Address Bus
This is the bus used to transmit the memory addresses specifying where data is to be sent to or retrieved from.
Data Bus
A bi-directional path for moving data and instructions between system components
Control Bus
A bi-directional bus to transmit command signals from the control unit to other parts of the processor
system bus
collective term for address, data and control bus
fetch decode execute cycle
The fetch-decode-execute cycle is the sequence of operations that are completed in order to execute an instruction.
Fetch phase:
- Address from the PC is copied to the MAR
- Instruction held at that address is copied to MDR by the data bus
- Simultaneously, the contents of the PC are increased by 1
- The value held in the MDR is copied to the CIR
Decode phase:
- The contents of CIR are split into operand and opcode
Execute phase:
- The decoded instruction is executed
Fetch
- The address of the next instruction is copied from the PC to the MAR
- The fetch signal is sent across the control bus. The contents of the MAR are transferred across the address bus.
- Instruction held at that address is copied to MDR by the data bus and the value held in the MDR is copied to the CIR.
- the PC increments by 1
Decode
The contents of the CIR are sent to the CU and divided. The operand contains the data or the address of the data upon which the operation is to be performed. The opcode specifies the type of instruction to be executed.
Execute
The appropriate instruction/ opcode is carried out on the data/ operand
program branch reason
occurs due to an if statement, function, procedure call or loop.
program branch result
the next instruction held in the PC is not carried out
Clock speed
Indicates the number of instructions the CPU can process per second.
The clock speed is determined by the system clock. This is an electronic device which generates signals, switching between 0 and 1. All processor activities begin on a clock pulse, and each CPU operation starts as the clock changes from 0 to 1. The clock speed is the time taken for one clock cycle to complete.
Clock speed Unit
Hertz (usually gigahertz)
Positives of increasing clock speed
you can carry out more instructions in a given time; improved performance
Negatives of increasing clock speed
more heat generated meaning computers must be cooled (either with heat sync/fan or water/oil cooling)