1.1 Hardware & Communication

Question 1

What happens in the FDE cycle?

Answer 1

1) The address in the PC is copied to the MAR
2) The address stored in the MAR is sent along the Address bus to the main memory where the data/ instruction is found
3) A “fetch” signal is then sent to the MDR via the control bus so it can fetch the contents of the memory address location which is then sent along the data bus
4) The contents of the MDR are copied to the CIR all while the contents of the PC are incremented
5) The contents are the CIR are decoded into operand and opcode
6) If more data is required for the instruction, it is fetched and passed to the accumulator
7) The instruction is then executed and the results are held in the accumulator or stored in the memory

Question 2

How does the CPU make efficient use of memory and clock cycles?

Answer 2

As an instruction is being executed, the next one is being fetched by the MDR and the PC is incrementing to memory address by one

Question 3

What does the Control bus do?

Answer 3

The Control Bus is unidirectional and sends control signals between the CPU’s registers and to other components

Question 4

What does the Data Bus do?

Answer 4

Is bi-directional and carries data or instructions from the main memory to the registers and vice versa.

Question 5

What does the Address Bus do?

Answer 5

Is unidirectional and carries the memory address of location being written or read to

Question 6

What does the CIR split instructions into?

Answer 6

Opcode and Operand

Question 7

What is opcode?

Answer 7

Is the part of an instruction that specifies the operation that is to be carried out

Question 8

What is operand?

Answer 8

Part of the instruction that:
Specifies the memory address of any addition data which is copied to the MAR
or
The actual data to be operated upon

Question 9

What is word size?

Answer 9

The number of bits that a CPU (registers) can manipulate at a time at a time.
Usually 8,16,32 or 64 bits

Question 10

What does increasing the word size do?

Answer 10

It allows for data to be manipulated at a greater speed. It also means that the CPU can fetch and keep track of more memory locations

Question 11

What happens if the width size of bus lines is the same as the word size?

Answer 11

Data can be transferred to and from memory in a single operation (clock tick), making the process more efficient

Question 12

What are the advantages and disadvantages of overclocking?

Answer 12

Advantages
- Can increase processing speeds especially in resource intensive tasks like video editing.

Disadvantages
- The CPU can be instructed to carry out instructions too quickly leading to corruption
- Places strain on the power supply

Question 13

What is a clock tick in terms of a wave?

Answer 13

When the electricity oscillates between 1 and 0 state

Question 14

What is a clock period?

Answer 14

The time between each rising edge (from 0 to 1)

Question 15

What are the advantages and disadvantages of using multiple cores?

Answer 15

Advantages
- Multiple programs can be run at the same time
- Resource intensive tasks take less time to process
Disadvantages
- Each core will take time in communicating to one another
- Sometimes a core will have to wait on the instruction of another core
OVERHEAD

Question 16

What is Parallel Processing and what is it also known as?

Answer 16

Parallel Processing AKA concurrent processing is when several processor cores are used at the same time to process multiple computations. It does this by splitting tasks into sub-tasks (threads) and splitting them between cores

Question 17

What are threads in parallel processing?

Answer 17

When a single task is split into smaller sub-tasks that are executed simultaneously by available processors

Question 18

What are all the types of cache memory and the difference between them?

Answer 18

Level 1 (Fastest, Smallest, Harvard Architecture)
Level 2 (Fast, Medium, Von Architecture)
Level 3 (Slower, highest capacity, shared by all cores to improve performance of L1 and L2)

Question 19

What is ‘overhead’?

Answer 19

The time lost due to communication between cores in parallel processing

Question 20

What is level 1 cache?

Answer 20

It is super-fast but small memory embedded on the CPU. The memory is split into instruction cache and data cache so data and instructions can be fetched simultaneously using Harvard Architecture.

Question 21

What is level 2 cache?

Answer 21

It is higher capacity cache (compared to level 1) and operates more slowly. It is located near the CPU or on another chip

Question 22

What is level 3 cache?

Answer 22

It is the highest capacity cache and aims to improve the performance of level 1 and 2 cache.
It is shared by ALL cores of the processor.

Question 23

What are the disadvantages of parallel processing?

Answer 23

• Programs are more complex to design and write compared to sequential processing
• To be efficient, synchronisation and communication between different sub-tasks (threads) must also be efficient which is difficult to achieve

Question 24

What is Von Neumann Architecture?

Answer 24

A system architecture where the data and instructions share the same memory and single data bus. They also have the same word length

Question 25

What is Harvard Architecture?

Answer 25

A system architecture where the data and instructions are held in separate memories and may have different word lengths. 2 busses are used for parallel access to data and instructions

Question 26

What is special about contemporary Processor Architecture and an example?

Answer 26

A modern CPU chips often incorporate aspects of both Von Neumann and Harvard architecture.

Question 27

What are the advantages and disadvantages of Von Neumann Architecture?

Answer 27

Advantages
- It is more cost effective
- There is a common bus for instruction transfer
- Overall simpler design (especially with the CU)

Disadvantages
- Two clock cycles are required to execute a single instruction
- CPU cannot access data and instructions at the same time
- Therefore less efficient

Question 28

What are the advantages and disadvantages of Harvard Architecture?

Answer 28

Advantages
- More efficient CPU as it can access instructions and read/write at the same time
- An instruction is executed per clock cycle

Disadvantages
- It’s more expensive than Von Neumann Architecture
- The control unit is more complicated due to 2 data busses
- Free data memory cannot be used for instructions leading to a less efficient memory

Question 29

What are the uses of Von Neumann Architecture?

Answer 29

Personal computers or small computers such as phones

Question 30

What are the uses of Harvard Architecture?

Answer 30

Used in micro controllers, digital signal processing and embedded systems

Question 31

What does RISC stand for?

Answer 31

Reduced Instruction Set Computer

Question 32

What does CISC stand for?

Answer 32

Complex Instruction Set Computer

Question 33

What does a RISC processor do?

Answer 33

It separates commands into a number of simple commands that can be executed in one clock cycle- it aims to process data in as little clock cycles as possible

Question 34

What does a CISC processor do?

Answer 34

It aims to complete a task in as few lines of code as possible by using circuitry that is able to execute a series of operations.

Question 35

What are the advantages and disadvantages of a RISC processor?

Answer 35

Advantages
- Simpler hardware is required
- Less complex circuitry and silicon meaning less expensive
- Lower energy consumption and heat produced

Disadvantages
- The compiler is required to do more conversation work
- More RAM is required to store the assembly instructions which, once used heavily, results in data bottlenecks
- Fewer address modes are available

Question 36

What are the advantages and disadvantages of a CISC processor?

Answer 36

Advantages
- Makes very efficient use of RAM
- The compiler is require to do less work
- Multiple addressing modes are available

Disadvantages
- Complex instructions take multiple clock cycles to complete
- Requires more complex hardware and circuitry
- More energy consumption

Question 37

What are the 3 types of screens?

Answer 37

LED (Light Emitting Diodes
OLED (Organic Light Emitting Diodes)
QLED (Quantum Light Emitting Diodes)

Question 38

What are the instructions executed on boot-up?

Answer 38

1) Self-diagnostic to check hardware is working
2) BIOS also checks the hard drive for bootstrap loader program
3) Bootstrap loader looks for and begins the OS
4) Hardware drivers are loaded to allow the OS to interact with the hardware
5) Log-in screen is displayed
6) Start-up programs (anti-virus software or printer software) are initiated

Question 39

What is the catch when increasing CPU threads?

Answer 39

While greatly boosting performance, some threads may need to wait on the result of another meaning the performance isn’t proportional to the number of cores.
This wait time is called ‘overhead’

Question 40

What is pipelining?

Answer 40

This is when the CPU is executing an instruction and fetchs the next instruction at the same time

Question 41

What is fragmentation and how does it arise?

Answer 41

Fragmentation is when a HDD stores the contents of a file/ program on physically different parts of the disk. This occurs when a file is removed and a bigger file attempts to take its place but then stores some of the data in that space and the rest at the end of the disk.

Question 42

What are the disadvantages of disk fragmentation?

Answer 42

The read-write arm will have to move across the HDD just to read a single file resulting in slower read times. The free space can also be located in different places on the HDD which results in slower write times too