Structure + function of a processor Flashcards
What is the CPU
Central Processing Unit - Runs programs by continuously fetching, decoding and executing instructions
What is the ALU
Arithmetic Logic Unit - Carries out the calculations and logical decisions.
What is the CU
Control Unit
- Sends out signals to co-ordinate how the processor works
- It controls how data moves around parts of the CPU and memory
- Instructions are decoded in the control unit
What is a register
A discrete piece of memory built onto the CPU that holds a single piece of data
What is the PC
Program Counter - Keeps track of the location of the line of machine code being executed
What is the MDR
Memory Data Register - Stores the data or instructions that are to be fetched from memory or sent to memory
What is the MAR
Memory Address Register - Stores the address of the data or instructions that are to be fetched from memory or sent to memory
What is the CIR
Current Instruction Register - Stores the most recently fetched instruction, which will be decoded and executed
What is the ACC
Accumulator - Stores the results of calculations made by the ALU
What are buses
The communications channels through which data can be sent around the computer
What is the purpose of the data bus
Carries data between the processor and memory
What is the purpose of the address bus
Carries the address of the memory location being read from or written to
What is the purpose of the control bus
Sends control signals from the control unit
Describe what happens when fetching instructions
- Contents of the PC are copied to the MAR
- The read signal is sent across the control bus and the contents of the MAR are sent across the address bus
- The contents of the memory location stored in the MAR are then sent across the data bus and stored in the MDR
- The contents of the MDR are then copied to the CIR
- The PC is incremented by one
Describe what happens when decoding instructions
- The contents of the CIR are sent to the CU
- The CU then decodes the instruction
Describe what happens when executing instructions
If the instruction is…
- for a memory location to be read from or written then the address stored within the instruction will be loaded into the MAR
- to carry out a calculation then the contents of the MDR and ACC are sent to the ALU and the results are sent back to the ACC
What is the clock speed
The frequency at which the clock generator of a processor can generate pulses
What is a core
A processing unit within the CPU
How does clock speed affect performance
Higher clock speed, the faster the CPU can run and the more instructions that can be processed every second
How does the number of cores affect performance
More cores, easier it is to run more things simultaneously. This means tasks that can share their work will run faster
What is cache
A fast memory that is built on or close to the CPU and is designed to reduce the need to access RAM which has slower access speeds
How does cache improve performance
Faster to access data than RAM
What is pipelining
Different parts of the CPU performing different parts of the fetch-decode-execute cycle on a sequence of instructions
Disadvantage of pipelining
If there is a branch instruction then the CPU has to try predict the next instruction to keep the pipeline full. If it gets it wrong then the pipelines have to get flushed and performance is degraded
What is a computer architecture
The approach taken in a computer’s design
What does Von Neumann architecture contain
- a single control unit
- a single arithmetic logic unit
- a single memory store that contains both instruction and data
What does Harvard architecture have
- a single control unit
- a single ALU
- a memory unit for data
- a bus for data
- a memory unit for instructions
- a bus for instructions
What is a thread
A sequence of instructions sent to the CPU to be processed
What is simultaneous multithreading
Allows two threads to run on each core at one time
What is ‘out of order execution’
Allows instructions to be executed ahead of when they usually would be if the required resources are needed, preventing delay.
What is RISC
Reduced Instruction Set Computing - A design approach where a CPU uses a small set of instructions
What is CISC
Complex Instruction Set Computing - Processors with a large instruction set with more complex instructions
What is a GPU
Graphics Processing Unit - Designed to perform the calculations associated with displaying graphics
Features of GPUs
- Instruction set specifically designed for graphics processing
- Can process pieces of data in parallel
Where can GPUs be used in apart from graphics
- Modelling physical systems
- Audio processing
- Breaking passwords
- Machine learning
What is parallel processing
When a computer carries out multiple computations simultaneously to solve a given problem
What is SIMD
Single Instruction Multiple Data - The same operation is carried out on multiple pieces of data, at one time
What is MIMD
Multiple Instructions Multiple Data - Different instruction are carried out concurrently on different pieces of data
What is hardware
Physical components of a computer system
What is meant by ‘peripheral’
Hardware attached to and used with a computer, but are not an integral part of it
What is magnetic storage and examples
Patterns of magnetisation are used to represent binary sequences.
e.g Hard disk drive, Magnetic tape
What is optical storage and examples
Uses a laser and by looking at its reflection, determines where there are pits on a surface, which represent binary.
e.g CD, DVD, Blu-ray
What is flash storage and examples
Uses a special type of read-only memory that can be overwritten
e.g USB, SD card and SSD
What is RAM
Random Access Memory - A type of primary memory that the CPU uses for programs and data in use. It loses its contents when power is loss
What is ROM
Read Only Memory - A type of primary memory that can only be read from. It retains its contents even when electrical power is lost. It’s often used to store start-up instructions on a computer
What is ROM often used for
The computer’s boot program/ BIOS
