Structure and Function of Processor

Question 1

What is a Register?

Answer 1

Extremely fast form of storage within the CPU to temporarily store small amounts of data as the CPU processes that data, with some having a specific purpose

Question 2

What is the ALU?

Answer 2

Arithmetic Logic Unit and performs arithmetic and logical operations

Question 3

What is the CU?

Answer 3

Control Unit which coordinates the input and output devices connected to the computer to execute the instructions and control the flow of signals within the buses

Question 4

What is the PC?

Answer 4

Program Counter and stores the address of the next instruction that will be fetched and increments after

Question 5

What is the Accumulator?

Answer 5

Temporarily stores the outputs of the ALU

Question 6

What is the MAR?

Answer 6

Temporarily stores the address of the next instruction to be fetched from main memory through the address bus

Question 7

What is the MDR?

Answer 7

Temporarily stores a copy of the data or instruction that was fetched from the main memory address that was pointed to by the MAR

Question 8

What is the CIR?

Answer 8

Current Instruction Register that holds the current instruction, ready to be decoded`

Question 9

What are busses?

Answer 9

A communication system within the CPU that transmits data between the registers and other computer components

Question 10

What is the Data Bus?

Answer 10

Carries data instruction around the systen

Question 11

What is the Address Bus?

Answer 11

Carries memory address from the MAR to main memory

Question 12

What is the Control bus?

Answer 12

Carries signals from the CU to coordinate inputs and outputs around the system

Question 13

What is the Clock?

Answer 13

With each tick of the clock, an instruction is processed

Question 14

What are the steps in the Fetch-Decode-Execute cycle?

Answer 14

1. The PC stores the address of the next instruction to be fetched, copied it into the MAR and increments the PC, which will point to the next instruction
2. The instruction found at the address the MAR has pointed to is copied to the MDR from main memory
3. The instruction from the MDR is copied to the CIR
4. The CU decodes the contents of the CIR and executed the instructions by sending signals to the relevant components

Question 15

Name the 6 main factors explaining CPU performance

Answer 15

Clock Speed, No. of Cores, Cache, RAM Capcity, GPU, Pipelining

Question 16

Explain the effect of clock speed on CPU performance

Answer 16

Clock allows 1 instruction to be executed with every tick of the clock, meaning the CPU is more coordinated.
The higher the clock speed, the more instructions can be executed in one second
Every time the clock ticks, the more power the CPU uses, meaning more heat is generated and so a larger heat sink, would be needed to keep the CPU at a stack temperature and not damage it

Question 17

Explain the effect of an increase in the number of cores on CPU performance

Answer 17

A core is complete processing unit within the CPU with its own registers
Each core can have its own cache to improve performance, along with a shared cache
Multi-tasking is far easier with a multi-core system as tasks can be performed simultaneously
Doubling the No. of cores does not necessarily double performance as there is extra processing over for coordination and programmers must specifically design their application for multi-core processors

Question 18

Explain the effect of cache on CPU performance

Answer 18

Cache is an extremely fast form of RAM on the CPU chip
Having a larger cache will speed up processing as the CPU can access data and instruction faster than it can from RAM, but is far more expensive
To speed up processing time, cache memory is used to store instructions or data that are either frequently used, have been used, or are about to be used, meaning they do not need to be fetched from the slower RAM
L1 Cache is the fastest, but smallest and is on the CPU chip. L2 Cache is slower but larger. L3 Cache is slowest but the largest. L2 and L3 can be found either on the motherboard or on the CPU chip

Question 19

Explain the effect of RAM capacity on CPU performance

Answer 19

RAM is used to store computer programs and data that are currently in use
If there is not enough RAM for the in-use programs, the CPU will use part of the secondary storage as a slower replacement for RAM
If more RAM is installed, there will be no need for virtual memory, but excess RAM will not increase performance

Question 20

Explain the effect of GPUs on CPU performance

Answer 20

Designed to handle graphical related tasks far faster than the CPU and the CPU will pass any graphics related processes to the GPU
GPU tasks can be run in parallel by issuing a single instruction to act on many pixels at the same time
Disadvantages:
- Expensive and does not improve CPU performance on all task, only graphical ones
- Uses a lot of power, meaning the computer may need as new PSU
- Generates a lot of heat and so needs loud cooling fans

Question 21

Explain the effect of pipelining on CPU performance

Answer 21

Technique of fetching an instruction whilst the prior one is being decoded and the one before is being executed
Speeds up CPU as multiple instructions can be processes at the same time, rather than one at a time

Question 22

Name the 5 main system performance factors

Answer 22

Faster CPU, GPU, RAM, Secondary Storage and Improving/Updating the OS

Question 23

Explain the effect of a faster CPU on system performance

Answer 23

Means more than one instruction can be processed per second, improving the overall speed and performance of the system

Question 24

Explain the effect of a GPU on system performance

Answer 24

Allows the CPU to pass graphical related tasks to the GPU as it can handle them far quicker

Question 25

Explain the effect of a secondary storage devices on system performance

Answer 25

Increasing the speed of secondary storage means data can be fetched faster and increasing the capacity means that when a file is copied from a different directory, there is enough storage and so the computer will not slow

Question 26

Explain the effect of improving/updating the OS on system performance

Answer 26

Updating the OS ensure it is efficient and secure, therefore quicker and malware can slow down the computer, so OS security updates help to prevent this

Question 27

Explain the Von Neumann CPU Architecture

Answer 27

When both data and software that are currently being used are stored in a shared memory

Question 28

What are the features of the Von Neumann Architecture

Answer 28

Enough memory to hold programs and data, making it easy to change tasks by loading a different program
The CU is responsible for handling movements of data and instructions around the computer
Data and instructions are carried by buses
There is an ALU, other registers and a way of inputting and outputting data from the computer

Question 29

What are the 4 main issues with the Von Neumann Architecture?

Answer 29

Shared Memory, Memory Leaks, Data Bus Speed, Data Bus Speed, Data and Instruction Fetch Rate

Question 30

Explain the issue of shared memory in the Von Neumann Architecture

Answer 30

A poorly written program can overwrite other programs in memory, making it more likely to crash that program as they share the same memory

Question 31

Explain the issue of memory leaks in the Von Neumann Architecture

Answer 31

A poorly written program may not release the memory it was using properly, resulting in insufficient memory available for other programs to store their data that can cause the computer to crash

Question 32

Explain the issue of data bus speed in the Von Neumann Architecture

Answer 32

The CPU runs faster than the transfer speed of the data bus, which could lead to a bottleneck, a solution is using cache, which keeps local copies of regularly used data and instructions within the CPU to prevent them from having to be transported through the data bus again

Question 33

Explain the issue of data and instruction fetch rate in the Von Neumann Architecture

Answer 33

The rate data needs to be fetched and the rate at which are fetched are very different, causing another data bus bottleneck

Question 34

Explain the Harvard Architecture

Answer 34

The memory is split into 2 parts, one for data and other programs with a different bus for each, meaning the CPU can be fetching data and instructions at the same time, preventing the Von Neumann bottleneck and leading to a lower change of program corruption and the speed of the bus can be optimised

Question 35

What are the disadvantages to the Harvard Architecture?

Answer 35

More physical space is needed as 2 buses must be installed instead of one
Handling 2 separate blocks of memory is more complex than handling 1