1.1.2 types of processor

Question 1

What is an instruction set and what are the 2 types?

Answer 1

• Set of all instructions written in machine code that can be recognised and executed by a given processing unit/CPU
• CISC AND RISC

Question 2

What is RISC

Answer 2

• Reduced Instruction Set Computing
• Instruction set made up of a small number of simple, fixed-length instructions/commands
• 1 instruction executed per clock cycle (designed to process simple instructions quickly)

Question 3

RISC examples of manufacturers

Answer 3

• ARM processors

Question 4

Where are RISC processors suitable for use and why?

Answer 4

• tablets, smartphones, and embedded systems, where it is not necessary to carry out complex instructions.

Question 5

Advantages of RISC

Answer 5

• simpler instruction design (all instructions are uniform in terms of execution time) makes pipelining easier to implement –> increases performance of RISC.
• simpler instructions mean programs run faster
• require less circuitry (fewer transistors) –> cheaper to design and produce, give off less heat, consume less power and leaves more room for general purpose registers and cache

-lower energy requirements

Question 6

Disadvantages of RISC

Answer 6

• several instructions needed therefore low-level programs for RISC processors are longer and take up more memory.
• Uses a lot RAM to store assembly instructions (more lines of code required). Can cause system bottlenecks if RAM is limited
• Emphasises software over hardware: high-level compilers that simplify and translate programmers code do more work
• larger code sizes (lower cycles per second)
• fewer addressing modes available

Question 7

What is CISC

Answer 7

• Complex Instruction Set Computing
• large number of complex instructions of variable length each taking multiple cycles to carry out

Question 8

Uses of CISC and examples of manufacturers

Answer 8

• most desktops computer and laptops
• Intel (x86) and AMD

Question 9

CISC advantages

Answer 9

• simpler software (compiler does less work as emphasis is on hardware)
• larger instruction set = work better with more intensive tasks (executes complex instructions and carry out a number of low-level operations as part of a single instruction)
• more specialised instructions means low-level programs for CISC processors take up less space in memory and are easier to translate to machine code.
• small code sizes, higher cycles per second
  -makes more efficient use of RAM (CISC requires less to store instructions)
  -multiple addressing modes available

Question 10

CISC disadvantages

Answer 10

• More circuitry (transistors) needed to execute complex tasks as it aims to complete in as few lines of assembly as possible. (expensive)
  -greater energy consumption, gives off more heat
• instructions can take multiple machine/clock cycles to execute —> makes pipelining difficult therefore CISC processing used for specialist computer systems

Question 11

what is a co processor?

Answer 11

• any additional processor used for a specialised task

Question 12

1. why did co processors emerge?
2. what do they do?

Answer 12

1. tech advanced —> demand increase on single CPU
2. improve overall speed of computer by executing concurrently with main CPU, aided by a highly bespoke set of electronics

Question 13

outline the 2 key differences between CPU and GPU

Answer 13

• central processing unit is more general purpose in contrast to graphics processing unit which is highly specialised
• CPU excels at performing complex operations on small data sets but GPU excels at performing simple operations on larger data sets

Question 14

What is the GPU’s bespoke design useful for (PP). And what applications can have improved performance from use of this

Answer 14

• Parallel Processing
• improves performance of video/graphic-intensive applications

Question 15

Which contemporary architecture does it make use of and why. SIMD, MIMD or Distributed Computing?

Answer 15

• SIMD
• because mass calculation associated to graphics processing take full advantage of parallel processing

Question 16

what does SIMD stand for

Answer 16

• Simple Instruction Multiple Data

Question 17

What does the contemporary architecture SIMD allow for

Answer 17

• parallel processing when a processor carries out single instruction on multiple data items at the same time

Question 18

give some uses of GPU’S

Answer 18

• weather modelling
• data mining
• machine learning
• linear algebra
• statistical analysis
• cryptocurrency to mine bitcoins
• graphics rendering

Question 19

what is memory mapped output

Answer 19

• facility for producing some form of basic visual output by mapping values in memory to pixels on a screen

Question 20

what is the benefit of a separate, dedicated processor for a computer running applications that require video/graphic-intensive applications?

Answer 20

• this design frees up main processor to handle other tasks.

Question 21

what do graphics cards contain

Answer 21

• own set of RAM and processor (GPU)

Question 22

Although GPUs best known for use in gaming, what other specialised purposes can they be used for (hint: ML) and why?

Answer 22

• machine learning applications.
• GPUs with 1000’s of cores = optimised to parallel process calculations, required for machine learning algorithms (usually good for one task)

Question 23

give an example of machine learning

Answer 23

• training a neural network

Question 24

why are operations such as 3D graphics rendering divided across multiple cores?

Answer 24

• as each core performs a small part of the whole operation.

Question 25

what are some main manufacturers of GPU’s

Answer 25

• Intel, NVidia, AMD

Question 26

What’s involved in rendering 3D image
Example: calculations like RGB for individual pixels

Answer 26

• All segments of image assigned XYZ co-ordinates (requires 3D arithmetic, stored as floating point)
• Every segment assigned texture/pattern
• Light source assigned + given an angle, brightness + how it falls on wireframe
• Camera source chosen for image

Question 27

what happens once calculations done?

Answer 27

• they’re run through every pixel of finished image from cameras perspective + generate 2D representation of 3D space

Question 28

what is a multicore processor

Answer 28

• Single chip/processor containing 2 or more independent processing units which can independently process instructions simultaneously

Question 29

what does CMPS stand for

Answer 29

• chip multiprocessors

Question 30

What is CMPS?

Answer 30

• when manufacturers integrate these cores (multicore processor) onto single physical chip (CMPS)

Question 31

why can be wrong to refer to single physical chip as CPU?

Answer 31

• as its actually a CMP containing multiple CPU cores

Question 32

1. what is a CMP with 2 cores called
2. what is a CMP with 4 cores called

Answer 32

1. dual-core processor
2. quad-core processor

Question 33

the performance of multicore processors is further enhanced by what 2 things?

Answer 33

1. on-chip shared cache
2. inter-core communication

Question 34

explain why double cores doesn’t always double performance

Answer 34

• overheads involved with inter-core communication (they have to take their turn when accessing cache + RAM; all of which uses up some of the potential speed that adding more cores gives you)
• some programs cant make max use of all cores

Question 35

Overall a multicore system should process _______ instructions _________ than a single core

Answer 35

1. multiple
2. faster

Question 36

what is parallel processing

Answer 36

• processing of program instructions by dividing them between multiple processor cores

Question 37

Improvement in _______________ gained by using multicore processors depends on ___________ taking advantage of ___________ ________________

Answer 37

1. performance
2. software
3. parallel
4. processing

Question 38

the extent to which parallel processing can speed up computation will be highly dependent on what 2 things

Answer 38

1. task being carried out
2. if software has been/can be designed and written to make use of parallel processing

Question 39

explain the benefit of parallel processing using multiple cores

Answer 39

• each processor (core) can execute a separate instruction at a time enabling multitasking as they process faster –> more processes completed per second

Question 40

EXAM QUESTION:
Some problems require a large amount of computing power that goes well beyond single CPU. Discuss the different approaches that can be taken to provide increasingly larger amounts of computing power + the types of problem they are suited to.

Answer 40

AO1: Knowledge and Understanding
- Processors have increasingly large clock speeds and can be overclocked.
- Processors can have multiple cores.
- Super computers can have co and/or multiple processors
- GPUs can be applied to problems other than graphics processing.
- Problems can be distributed across a number of computers working together.

AO2.1: Application
- multiple cores can speed up smaller problems but won’t be enough for larger problems.
- Supercomputers are prohibitively exceptionally expensive to buy + run for all but large organisations.
- GPUs becoming cost efficient way of tackling problems as they tend to have large number of cores so can run on highly paralleliseable problems, only where same instruction being applied to multiple pieces of data (SIMD)

AO3.3: Evaluation
- Increased clock speed = limited to smaller problems. doubling clock speed would only halve time taken.
- Parallel processing isn’t suited to all problems as most are only partially parallelisable.
- GPUs suited to a subset of science/ engineering problems where same calculation repeated on multiple data sets.
• software (shader) that renders the display (1).

Question 41

What is a parallel processor system?

Answer 41

• one which simultaneously uses several processors to perform single task which may be split into a number of sub-tasks each of which may be processed by any available processor.

Question 42

what is sequential processing

Answer 42

• when instructions carried out one at a time in order which they are received

Question 43

what’s a disadvantage of sequential processing

Answer 43

• very slow