The Processor Flashcards
Purpose of the CPU
- To process machine instructions
- Carry out the fetch-decode-execute cycle
3 Main components of CPU
CU, ALU, RAM
What is the CU?
Control Unit: Sends control signals to other components - responsible for organising the FDE of instructions - controls input/output devices - communicates with all parts of the CPU
What is the ALU?
Performs calculations and makes logical decisions
What is RAM?
Holds the data and instructions for the currently running programs
What are registers?
Stores the programs which are needed instantly e.g. software applications
5 registers
1) Accumulator
2) PC
3) CIR
4) MDR
5) MAR
Accumulator
Holds the data currently being processed - results of calculations carried out by ALU
Program Counter
Holds the memory address of the next instruction to be executed - increments the next instruction to be fetched
Current Instruction Register
Stores the address of the instruction currently being executed
Memory Data Register
Stores data being transferred temporarily - all data to and from memory must travel down the data bus and pass through the MDR
Memory Address Register
Stores the address of the memory location currently in use - sends address to memory down the address bus
Address Bus
Carries the address of the memory locations
Data Bus
The contents of the instruction are carried
Control Bus
Informs whether the info is read or write control signals
Bus Width
The number of wires that make up a bus - determines the range of instructions that can be transmitted
Fetch Stage
- PC register displays the address in RAM of the next instruction to be processed
- This value is copied into the MAR
- The PC is incremented by 1
- This prepares the CPU for the next instruction to be fetched
- The CPU checks the address in RAM which matches the address held in the MAR
- The instruction in RAM is transferred to the MDR
- The instruction in the MDR is copied into the CIR
Decode Stage
The instruction in the CIR is understood and decoded - CU sends signals using the 3 busses
Execute Stage
Any result of an execution is stored in the ACC register
Clock Speed
How many CPU cycles can be run per second - the bigger the number the more cycles can be run per second
Overclocking
Making a computer or component operate faster than the clock frequency specified by the manufacturer - system can become unstable and there is a risk of damage due to excessive heat generation
Cache
Cache memory is used as the RAM is significantly slower than the speed CPUs operate - fast memory built into the processor reducing the distance data has to travel to it
Cores
Additional processors
Increasing the number of cores
Ensures cycles can be run simultaneously
Increasing cache size
Ensures more frequently used programs can be accessed much faster
Multicore Processor
Single chip containing two or more independent processing units - each core can FDE its own instructions
Chip with 2 cores
Dual-core processor
Chip with 4 cores
Quad-core processor
Limitation of multicore processing
Double the number of cores does not mean double the performance (overheads involved with inter-core communication, some programs cannot make maximum use of all cores
Parallel Processing
The processing of program instructions by dividing them between multiple processors or processor cores
Limitation of parallel processing
The extent parallel processing can speed up computation depends on the task being carried out and if the software is designed to make use of parallel processing
Co-processor
Any additional processor used for a specialised task - improves the overall speed of a computer by executing concurrently
Graphical Processing Unit (GPU)
- Run slower than a CPU core
- Highly specialised - superior in speed and efficiency for certain tasks
- Better than CPUs for larger data sets
