Unit 5 - Computer organisation and hardware

Question 1

What is the definition of a computer system?

Answer 1

A computer system is a system that takes in a set of inputs, processes them and outputs a set of outputs.

Question 2

What are the four component types contained within the CPU?

Answer 2

• Processor
• Main memory
• Address, control and data buses
• I/O controllers

Question 3

What allows an I/O device to interface with the computer?

Answer 3

I/O devices use I/O controllers, named device drivers, as a bridge between them and the computer.

Question 4

Tasks of an I/O controller:

Answer 4

• Convert signals from peripheral device into a format the computer can process and vice versa
• Receive I/O signals from the CPU and send device-specific signals to the device
• Manage data flow to and from the device

Question 5

What are the three buses and their purposes?

Answer 5

• Control bus sends control signals
• Data bus sends data
• Address bus sends memory addresses

Question 6

In what direction does the address bus send memory addresses?

Answer 6

The address bus only sends addresses from the processor to all the CPU components.

Question 7

In what direction does the control bus send signals?

Answer 7

The control bus sends signals between the processor and all CPU components, in both directions.

Question 8

In what direction does the data bus send data?

Answer 8

The data bus sends data from the processor to output devices and memory and sends data from input devices to memory.

Question 9

Give two examples of control signals.

Answer 9

• Memory read
• Memory write
• Bus request
• Bus grant
• Clock

Question 10

What are the units that memory is divided up into?

Answer 10

Words.

Question 11

What is a word (CPU)?

Answer 11

A word is a fixed-size unit of data handled as an instruction by the processor.

Question 12

What is the width of a data bus?

Answer 12

The width of a data bus is the number of wires it contains and the word length that can be transferred in a single operation.

Question 13

What does the width of the address bus decide?

Answer 13

The width of the address bus decides the maximum possible number of memory addresses of the system.

Question 14

What is the stored program concept?

Answer 14

The stored program concept is the loading of machine code instructions into memory, where they can then be executed immediately by the processor in a sequential order.

Question 15

What is the difference between Harvard architecture and Von Neumann architecture?

Answer 15

Harvard architecture grants a separate bus of data and instructions, whilst Von Neumann architecture requires them to both share a single bus.

Question 16

When is Harvard architecture most commonly used and why?

Answer 16

Harvard is most commonly used in embedded systems that need to perform specialist functions. This is because speed is often important and the cost is less of a concern.

Question 17

What are the five components within the processor? (two of them are kind of the same)

Answer 17

• Arithmetic logic unit
• Control unit
• Clock
• General purpose registers
• Dedicated registers

Question 18

How does the control unit synchronise the activity of the components in the processor?

Answer 18

The control unit decodes the instruction and identifies the individual steps such as fetching address and fetching data. Each step is then synchronised using regular pulses from the system clock.

Question 19

What are the five dedicated registers within the processor?

Answer 19

• Control Unit
• Memory Address Register
• Memory Buffer Register
• Current Instruction Register
• Status Register

Question 20

What are the four steps of the fetch section of the fetch decode execute cycle?

Answer 20

1) Address of next instruction is copied from PC to MAR.
2) PC is incremented by 1.
3) Instruction in location specified by MAR stored in MBR.
4) Instruction transferred from MBR to CIR.

Question 21

What are the three steps of the decode section of the fetch decode execute cycle?

Answer 21

5) Instruction in CIR is decoded.
6) Additional data required for instruction (if any) is fetched from memory.
7) This data is then passed to the registers.

Question 22

What are the three steps of the execute section of the fetch decode execute cycle?

Answer 22

8) Instruction is executed by the ALU.
9) Registers are used to store intermediate data or results.
10) Result is stored in accumulator or general purpose memory.

Question 23

Factors that affect performance of a CPU:

Answer 23

• Clock speed
• Cache memory
• Number of cores
• Word length
• Bus widths

Question 24

The range of operations such as ADD, SUBTRACT and NOT available to a processor are decided by the… ?

Answer 24

Instruction set.

Question 25

What factor decides how many bits can be used for instructions in a processor’s instruction set?

Answer 25

The word length of the processor.

Question 26

What part of an instruction is the addressing mode found within?

Answer 26

The addressing mode of an instruction is a part of the operation code.

Question 27

What are the two options for the addressing mode of an instruction?

Answer 27

• An actual value (Immediate)

- An address in memory (Direct)

Question 28

What makes primary storage different to secondary? (not access speeds)

Answer 28

Primary storage, usually RAM, is volatile, whilst secondary storage is non-volatile.

Question 29

What are the five key characteristics to consider when looking at secondary storage devices?

Answer 29

• Durability
• Portability
• Cost
• Capacity
• Read/write speed

Question 30

How is data stored on a hard disk?

Answer 30

Data is stored in sectors of the platter, which are found in a concentric shape. This data can then be read by a read/write head while the disk is spinning.

Question 31

How is data stored on a magnetic storage device?

Answer 31

Magnetic particles on the disk are either negatively or positively polarised. Changes in polarisation will create an electromagnetic pulse, which is read as a binary 1.

Question 32

What is disk latency?

Answer 32

Disk latency is the time taken to read/write disk data.

Question 33

Factors that affect disk latency:

Answer 33

• Seek delay (time taken for the head to move the correct concentric track)
• Rotational delay (time the disk takes to rotate the correct sector under the head)
• Transfer time

Question 34

How is information stored onto a CD?

Answer 34

A high-power laser burns pits into the CD.

Question 35

How is information read from a CD?

Answer 35

A low-powered laser fires towards the CD and the laser will be reflected by any part of the CD that isn’t flat, a.k.a when it is transitioning from a pit to a land. Deflections are read as a binary 1.

Question 36

What is different between optical disk formats?

Answer 36

They all use slightly different techniques to achieve a differential between a “pit” and “land” depending if they are read-only, re-writable etc.

Question 37

How can the information density of an optical disk be improved?

Answer 37

The pits can be etched in with a laser of lower wavelength, which allows the spiral track to be wound tighter.

Question 38

How does flash memory store data?

Answer 38

Flash memory uses NAND flash memory cells. They contain floating gate transistors, surrounded by oxide layers, can trap or release charge. Trapped charges are read as binary 0’s and remain trapped when power is lost.

Question 39

Advantages of solid state drives:

Answer 39

• Faster access speed due to no moving parts
• More durable for same reason
• Lower power consumption
• Silent
• Lighter

Question 40

How can the information stored in Solid State Drives be modified?

Answer 40

The whole memory block has to be reset then rewritten with the new changes. The new data is temporarily stored in RAM and is removed once the data is written back into the SSD.