1.2 CPU Performance

Question 1

What affects the performance of the CPU?

Answer 1

Clock speed, Processor cores and cache

Question 2

What is clock speed?

Answer 2

How many cycles per second (e.g 2GHz is around 2 billion instructions a second) which is measured in hz

Question 3

What are cores?

Answer 3

Processing units (ALU)

Question 4

What is cache?

Answer 4

Memory on the CPU that is faster than RAM but is slower than registers

Question 5

How does clock speed affects the performance of the CPU?

Answer 5

The rate of instructions is determined by the clock meaning that if the clock is faster then there are more instructions happening per second

Question 6

Processor speed:

Answer 6

1 kHz = 1000 cycles per second
1 MHz = 1,000,000 cycles per second
1 GHz = 1,000,000,000 cycles per second

Question 7

How does multi-core processing affect the performance of the CPU?

Answer 7

• It has the potential to perform more instructions at the same time
• However in order for this to be useful, the software has to take advantage of all the cores for the performance to be better

Question 8

How does cache memory affect the performance of the CPU?

Answer 8

Cache can be accessed faster than RAM and this impacts the performance because instructions and data can be fetched faster and if they are needed again soon it is very easy to get compared to RAM and speeds up the execution

Question 9

What are the levels of cache?

Answer 9

Level 1, Level 2, Level 3

Question 10

What is L1 cache?

Answer 10

Extremely fast cache but small(2-256KB), each core will have its own level 1 cache

Question 11

What is L2 cache?

Answer 11

Very fast but a little slower than L1 cache and has around 256KB to 8MB. Most cores would have L2 cache

Question 12

What is L3 cache?

Answer 12

Slowest type of cache but is still faster than RAM. Located in the CPU and stores around 4MB to 50MB and is shared amongst all of the cores on the processor.

Question 13

What are the benefits of cache?

Answer 13

• L1 50% of the time is used and L2 is used 90% of the time.
• The size of L2 cache is a major factor in determining the performance of the CPU
• The data used most often is stored in L1 cache

Question 14

What might be better use for a low end system?

4 cores at 2GHz or 2 cores at 4GHZ

Answer 14

2 cores at 4GHz because the program the computer uses may not utilise the full 2 cores and the 2 cores run faster than than the 4 cores

Question 15

What might be better use for a gaming system and a workstation?
4 cores at 2GHz or 2 cores at 4GHz

Answer 15

4 cores at 2GHz because most modern computer programs utilise as many cores as they can use

Question 16

How many cycles does 4 cores at 2GHz do?

Answer 16

8 billion cycles

Question 17

How many cycles does 2 cores at 4GHz do?

Answer 17

8 billion cycles

Question 18

Levels of cost per byte and access speed of memory

Answer 18

1. CPU registers
2. L1 cache, L2 cache, L3 cache
3. Physical RAM (main memory)
4. Disc storage (Virtual RAM, Hard Drive etc.)

Question 19

Levels of capacity

Answer 19

1. Disc storage
2. Physical RAM
3. Cache
4. CPU registers

Question 20

What is an embedded computer?

Answer 20

An embedded computer is a single microprocessor that includes RAM, ROM and a CPU and is frequently used in devices that have simple inputs

Question 21

Give an example when you would need an embedded system

Answer 21

A satnav needs to know how to communicate with a satellite

Question 22

How fast are CPUs in embedded systems?

Answer 22

Slow

Question 23

What features are in software of embedded systems?

Answer 23

Only has one purpose and cannot install new software

Question 24

What features are in storage of embedded systems?

Answer 24

Programs are stored on ROM

Question 25

How reliable are embedded systems?

Answer 25

Very reliable as they are simple operations that they are doing

Question 26

3 examples of an embedded system

Answer 26

Satnav, microwave, dishwasher