(P2) Fundamentals of Computer Architecture

Question 1

Describe the fetch part of the FDE cycle.

Answer 1

Contents of PC are transferred to MAR.
Address bus is used to transfer this address to main memory.
Contents of addressed memory location are loaded into MDR.
Transfer of content uses data bus.
Increment contents of PC.
Increment PC and fetch simultaneously.
Transfer content of MDR to the CIR.

Question 2

Describe the decode part of the FDE cycle.

Answer 2

Decode instruction held by the CIR.
The control unit decodes the instruction.
Instruction split into opcode and operands.

Question 3

Describe the execute part of the FDE cycle.

Answer 3

If necessary, data is fetched.
The opcode identifies the operation to be carried out by the processor.
Execute instruction by relevant part of processor.
Result stored in accumulator.
Status register is updated.
If there is a jump or branch, update PC.

Question 4

Give two advantages of using Harvard Architecture compared to Von Neumann Architecture.

Answer 4

Instructions and data memory can have different word lengths.
Instructions and data can be accessed at the same time.

Question 5

Describe the role of the control unit.

Answer 5

Executes instructions.
Synchronises operation of processor.
Sends control signals to other components.
Control the transfer of data between registers.
Handles interrupts.

Question 6

What is cache memory?

Answer 6

Memory that can be accessed quickly and is close to the processor.

Question 7

What is cache memory used for?

Answer 7

Storing frequently used data.

Question 8

Why does an increase in cache increase the performance of a processor?

Answer 8

More instructions can be stored in cache.
Fewer fetches from main memory are required.

Question 9

Describe the role of interrupts.

Answer 9

Allows currently executing process to be suspended so that any devices that need immediate attention of the processor can be dealt with.

Question 10

Explain why the volatile environment (the contents of registers) must be saved before an interrupt is serviced.

Answer 10

So that the current running process can be returned to.
As the code that deals with the interrupt will change values.

Question 11

What is immediate addressing?

Answer 11

The operand is the value that instruction should use.

Question 12

Explain the effect of increasing the width of a data bus.

Answer 12

Speed at which data can be retrieved will be increased.

Question 13

Explain the effect of increasing the width of an address bus by 1 bit.

Answer 13

Amount of available memory locations will double.

Question 14

Explain the advantages of using a laser printer.

Answer 14

Low cost per printed page.
Toner is cheaper per page than ink.
Toner does not expire as quickly as ink.

Question 15

Explain the advantages of a wireless printer.

Answer 15

Easy to share priner between many devices.
No need for cabling.

Question 16

Describe how a laser printer works.

Answer 16

Bitmap of inage built in memory from page description.
Negative charge applied to photosensitive drum.
Laser beam directed at drum.
Mirror used to direct laser beam.
Where laser strikes drum charge is reversed.
Negative charge applied to toner.
Toner sticks to drum and toner transfers to it.
Positively charged transfer roller assists transfer of toner from drum to paper.
Heat fuses toner onto paper.
For coloured printing, four drums are required.

Question 17

Describe how a digital inage could be captured by a digital camera and compressed using run length encoding.

Answer 17

Light enters through lens onto sensor chip.
Each sensor produces an electrical signal.
Signal represents a pixel.
An ADC converts measurements of light intensity into binary.
Coloured filter is applied to generate separate data values for red, blue and green components.
Pixels are recorded as an array.

Question 18

Describe how an optical disk drive works when used to read data from CD-ROM or DVD-ROM.

Answer 18

Light is shone at the disk.
Light is focused on a spot on the track.
Some light is reflected back from disk.
Amount of light reflected back is measured.
Disk spins at constant linear velocity.
Data is stored on spiral track.
Continuation of land/ pit reflected light whereas transition between land and pit indicates a 1 and the continuation of land/ pit represents 0.

Question 19

Describe how a laser printer prints and inage onto paper.

Answer 19

Print drum is coated in positive static charge.
Printer generates bitmap of page from the data.
Laser beams shone by rotating octagonal mirror.
Laser is modulated.
Laser reverses electric charge on drum, where image should be dark. Toner is given positive charge. Charged drum pocks up toner.
For drum mechanisms, one for each colour.
Toner is transferred from drum to paper.
Toner is stuck to paper by heat rollers.

Question 20

Why is translation necessary?

Answer 20

Processor can only execute machine code instructions.
High level languages need to be converted into machine code to be executed.

Question 21

What is the difference between how a compiler and interpreter would translate a program?

Answer 21

Complier analyses the whole program.
Interpreter analyses program line by line.
Compiler produces object code.
Compiler will not translates any of the code if it encounters an error.
Intepretet translates program each time it is executed.
Intepreter executes each line immediately after translating.

Question 22

What does RAM stand for?

Answer 22

Random Access Memory

Question 23

What does ROM stand for?

Answer 23

Read Only Memory

Question 24

What is the function of main memory?

Answer 24

Store program instructions and frequently used data.

Question 25

What is contained within main memory?

Answer 25

RAM and ROM

Question 26

Explain an advantage of main memory over secondary storage

Answer 26

Main memory is faster than secondary storage so frequently used data in RAM and ROM helps the processor to execute instructions quickly.

Question 27

What is a bus?

Answer 27

Series of parallel wires that connect internal components, allowing signals to be passed.

Question 28

The number of parallel wires in a bus is called it’s…

Answer 28

Width

Question 29

What is the function of the address bus?

Answer 29

Transport memory addresses, specifying where data is to be sent and retreived from.

Question 30

What happens if you increase the width of the address bus?

Answer 30

Increases range of addresses that it can specify

Question 31

True or false: Adding a single wire doubles the number of addressable memory locations.

Answer 31

True

Question 32

What is an addressable memory

Answer 32

A portion of memory that can be accessed by its address.

Question 33

What is the function the data bus?

Answer 33

Sends data and instructions to and from the different components of the computer system.

Question 34

What happens if you increase the width of the data bus?

Answer 34

Increases the volume of data that can be transferred over the bus at any time

Question 35

What if the function of the control bus?

Answer 35

Used to carry control signals that regulate the operation of the computer system. Carries the computer’s clock signal.

Question 36

What are the functions of I/O controllers?

Answer 36

Control communication of data between the processor and external hardware devices.

Question 37

Describe Harvard Architecture.

Answer 37

Two separate memory locations: one for instructions and the other for data.
Memory used for instructions could be read only so instructions cannot be altered.
Embedded systems such as digital signal processing.

Question 38

Describe Von Neumann Architecture.

Answer 38

Instructions and memory stored together in the same memory.
Performs worse than Harvard.
Same buses have to be shared for fetching both instructions and data.
Used in everyday purpose computer system.

Question 39

What does serially mean?

Answer 39

Instructions are fetched and executed in order.