Structure and Function of Processor Flashcards
What are the 4 functions of the Control Unit? (CU)
Coordinates all activities of the CPU.
Directs flow of data between CPU and other devices.
Decodes instructions
Sends read/write requests to main memory on the Control bus
What is the function of the PC?
Holds the address of the next instruction to be executed.
Can be changed to address in CIR if operation is a Jump.
What are the 2 functions of the Memory Address Register? (MAR)
Holds the address of the location in memory to be read from/written to.
Sends these addresses to RAM down the Address bus
What is the function of the Memory Data Register? (MDR)
Temporarily stores data which is read from/to be written
Sends/receives data down the Data Bus
What are the 3 functions of the Current Instruction Register? (CIR)
Holds the current instruction being executed
If contents of MDR are an instruction, it is copied to CIR
Contains the opcode and operand of the current instruction.
What are the 2 functions of the Arithmetic Logic Unit? (ALU)
Performs arithmetic and logical operations on data
Arithmetic -> +, -, *, /
Logical -> <, >, !=, ==
Boolean -> AND, OR, NOT, XOR
What is the 4 functions of the Accumulator? (ACC)
Holds all input/output
Temporarily stores calculations from ALU for quick retrieval.
Stores data from MDR and RAM
Checked for conditional branching (e.g. BRZ)
What is a register?
A small piece of memory used for storing data within the processor
What are buses?
Sets of wires that connect two components together so that they can communicate
What is the function of the Address Bus?
Carries memory addresses that identify where data is being read from/written to
Uni-Directional (1 way)
What is the function of the Data Bus?
Carries the binary 1s and 0s that make up the actual information being transmitted around the CPU
What is the function of the Control Bus?
Carries commands and control signals to and from every other component in the CPU.
e.g. Memory read or memory write
Explain the FETCH process of the FDE cycle
Address stored in PC is copied to MAR.
PC increments by 1.
That address is then sent along the address bus to RAM, where it waits for a signal form the control bus.
Then CU sends a READ signal along the control bus to RAM.
Now that RAM knows the contents need to be READ, it sends the data down the data bus to the MDR.
Data in MDR copied over to CIR
Explain the DECODE process of the FDE cycle.
Instruction in the CIR is decoded into Opcode and Operand.
Opcode: What to do
Operand: What/Where to do it to
Explain the EXECUTE process of the FDE cycle.
The Opcode and Operand are sent from the CIR to the ALU where the instruction is carried out.
Results stored in ALU
What are 3 factors affecting the performance of the CPU?
Clock Speed
Number of Cores
Cache
What are the 3 buses in the CPU collectively known as?
The System Bus
What is the function of the System Clock?
Synchronises the operation of the Processor.
What is Clock Speed?
The max number of FDE cycles per second.
Usually measured in GHz
What is a Core?
A separate processor that is able to run its own FDE Cycle
Why does Number of Cores affect CPU performance?
A CPU with more cores can complete more FDE cycles at any given time.
In theory, a computer with dual cores can complete tasks 2x as fast a single core computer.
What is the downside of Number of Cores?
Not all programs are able to utilise multiple cores efficiently as they have not designed to do so
What is Cache?
Fast, small capacity set of memory that sits close to the processor
Stores the most frequently used instructions and data.
L1: Part of core circuitry - smallest and fastest
L2: Shared by cores
L3: On motherboard
L4: Near/on the processor - largest and slowest
What is Pipelining?
Allows concurrent processing of multiple instructions!!!
Allows one instruction to be fetched as the previous one is being decoded, and the one before that being executed.
Meaning more instructions can be carried out in a set amount of time.
