Unit 1 Lesson 1 - Processor Components Flashcards
What are the 5 different Registers in a CPU?
Program Counter (PC)
Memory Address Register (MAR)
Memory Data Register (MDR)
Current Instruction Register (CIR)
Accumulator
What is the CPU and what does it do?
The CPU is the Central Processing Unit which processes instructions.
What components does the CPU have?
Control Unit
Buses
Arithmetic-Logic Unit (ALU)
Dedicated Registers
What is the Control Unit?
Part of the processor that coordinates the activity of other components.
Control signals are sent along the control bus between Control Unit and other components of computer
What is a Bus?
Buses consist of a series of connectors that transfer signals between internal components.
(typically consist of 8, 16, 32, 64 lines)
Describe the purpose of the Control Bus
A Bi-Directional Bus (Signals can be sent both directions) which transmits signals between internal and external Components.
Co-ordinates use of address & data buses and provides status information between system components.
What Control Signals are sent on the Control Bus?
Bus Request - Shows device requesting use of Data bus
Bus Grant - Shows CPU has granted access to Data bus
Memory Write - Data written to addressed location using this bus
Memory Read - Data is read from a specific location to be placed onto Data bus
Interrupt Request - Shows device requesting Processor time
Clock - used to synchronise operations
Describe the purpose of the Data Bus
Bi-Directional (Data can be sent either direction) bus used for transporting data and instructions between components.
Describe the purpose of the Address Bus
Bus is used to retrieve memory addresses specifying where data is to be sent or retrieved from.
Width of this bus is proportional to number of addressable memory locations
What is the System Bus?
Collective name for the Data bus, Address bus, Control bus
What is the purpose of the Accumulator?
A register which stores results from the ALU (Arithmetic Logic Unit).
What is a Register in a processor?
Super-Fast memory which temporarily stores data
Describe what happens in the Fetch stage of FDE (Fetch Decode Execute) Cycle.
- Address in Program Counter copied to the MAR
- Instruction stored in the location addressed by MAR is transferred to Main Memory then to MDR
- Simultaneously, PC contents increments
- Instruction transferred from MDR to CIR
Describe what happens in the Decode stage of FDE (Fetch Decode Execute) Cycle.
- Instruction held in CIR is decoded
- Split into operand and opcode to determine type of instruction. Additional data (if needed) is fetched from Main Memory.
- Passed to accumulator
Describe what happens in the Execute stage of FDE (Fetch Decode Execute) Cycle.
The Instruction is executed and result is held in Accumulator or Main Memory.
What is meant by opcode?
The opcode specifies the operation that is to be carried out.
What is held by the operand?
Address of data to be used, which is then copied to MAR
or
The actual data to be operated on, which is then passed to the MDR
What does the width of the Address Bus mean?
The width of the Address Bus represents the maximum possible memory addresses of the system.
Example: an 8-bit address bus has maximum number of memory addresses as 2^8 = 256
What does width of the Data Bus mean?
It determines the maximum size of an operand in an instruction.
