Chapter 2 - Processor performance

Question 1

What are the 3 main factors which affect processor performance?

3 Marks

Answer 1

» Clock speed
» Number of cores
» Amount/type of cache memory

Question 2

What is the definition of clock speed?

1 Mark

Answer 2

» It is the number of FDE cycles the CPU can process per second and it is measured in hertz (Hz)

Question 3

Why can the CPU not perform operations faster than the clock cycle?

Answer 3

» Each CPU operation starts as the clock changes from 0 to 1, therefore cannot perform operations faster than the clock cycle

Question 4

What is clock speed measured in ?

1 Mark

Answer 4

» Gighertz

Question 5

What will be the consequence for a greater clock speed?

3 Marks

Answer 5

» More instructions will be executed
» As more there is a greater rate of FDE cycles happening per second
» So the program takes less time to run

Question 6

What is the key feature of the Von Neumann architecture?

To do with the instructions

Answer 6

» Instructions are fetched and executed one a time in a serial manner

Question 7

What does a Dual - core processor have?

Answer 7

» 2 Processor linked together in the same integrated circuit

Question 8

» What is the benefit of having a dual core processor?

Answer 8

» Each core is able to process a different instruction at the same time with its own F-D-E cycle

Question 9

What is one key fact about cache?

Answer 9

» It is much faster than RAM

Question 10

What happens when the cache fills up?

1 Mark

Answer 10

» Unused instructions or data still being held are replaced with more recent ones

Question 11

How many types of cache level are there?

1 Mark

Answer 11

» L1
» L2
» L3

3

Question 12

What is the fastest type of cache?

Answer 12

» Level 1 cache,
» But it is very small, usually between 2-64 Kb

Question 13

What is Level 2 cache?

Answer 13

» Slower than level 1,
» But has a bigger size, approximately between 256Kb-2MB

Question 14

What is the final cache level?

Answer 14

» Level 3

Question 15

Why do some processors use pipelining?

2 Marks

Answer 15

» It is a technique used by some processors to improve performance
» Reduces latency as CPU is not idle while waiting for the next instruction

Question 16

What happens without pipelining?

1 Mark - To do with the FDE cycle

Answer 16

» The steps in the FDE cycle takes place one after the other, while one instruction is being fetched, the ALU is idle

Question 17

What is the definition of pipelining?

3 Marks

Answer 17

» Allows the next instruction to be fetched at the same time as the previous instruction is being decoded, and the one before that is being executed
» It is the concurrent processing of multiple instructions
» Increases speed of execution

Question 18

What are the 2 types of processor pipelining?

1 mark

Answer 18

» Instruction pipelinining
» Arithmetic pipelining

Question 19

What is the instruction pipeline?

1 Mark

Answer 19

» Consists of the stages which an instruction is moved through the processor
» Such as it being fetched, buffered and then executed

Question 20

What is the arithmetic pipelining?

1 Mark

Answer 20

» Represents the parts of an arithmetic operation that can be broken down and overlapped as they perform

Question 21

What does each word, or group of bytes in memory have?

1 Mark

Answer 21

» Its own specific address

Question 22

How does the processor read a word of data from memory?

Answer 22

» Puts the address of the desired word on the address bus

Question 23

What does the wdith of the address bus determine?

1 Mark - to do with memory

Answer 23

» The maximum possible memory capacity of the system

Question 24

What happens if the address bus consists of only 8 lines?

1 Mark - Talk about maximum address

Answer 24

» Maximum address it can transmit is 255
» Maximum memory capacity is 256, including the address 0

Question 25

What is the purpose of the data bus?

Answer 25

» Transmits the data held in a word of memory, between processor components and memory

Question 26

What happens if the bus is only 17 bits wide?

Answer 26

» A word cannot hold an integer greater than 2^16 - 1, or more than characters

Question 27

What is the affect of a wider data bus?

1 Mark

Answer 27

» It can transmit larger values, or more characters at a time, or allow more bits per instruction

Question 28

How will the opcode be expressed in assembly language?

Answer 28

» Using a mnemonic

Question 29

What are some examples of how opcode will he expressed in main memory?

4 Marks

Answer 29

» ADD - Additions
» SUB - Subtraction
» LDA - Load into accumulator
» BRA - Branched into the accumulator

Question 30

How many bits is the opcode in a 16bit word?

Answer 30

» Only 6 bits

Question 31

How many bits in the operand for a 16bit word?

Answer 31

» 8 bits

Question 32

How many bits for the addressing mode for a 16bit word?

Answer 32

» 2 bits

Question 33

What can cause the pipeline to be flushed?

2 Marks

Answer 33

» iterations can cause the value in the program counter to change
» As the wrong instruction can be fetched/decoded which causes the pipeline to flush

Question 34

What is a core?

Answer 34

» A distinct processing unit within the CPU