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a-level computer science > 4.7 > Flashcards

4.7 Flashcards

1
Q

What is bus width?

A

The number of wires a bus has.

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2
Q

What is the system bus?

A

The bus that connects the processor, main memory and the i/o controllers.

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3
Q

What is the system bus made from?

A

The data bus, the address bus and the control bus.

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4
Q

How does the cpu interact with i/o devices?

A

Via the system bus which connects to an i/o controller. This controller then connects to the peripheral device.

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5
Q

What is a peripheral device?

A

A device that is connected to the computer system but is not under direct control of its processor.

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6
Q

What is the data bus?

A

Carries data bidirectionally between the processor and memory.

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7
Q

What is the control bus?

A

A bidirectional bus that allows the control unit inside the cpu to send commands and status information between components.

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8
Q

What is the address bus?

A

The address bus carries addresses from the cpu to memory.

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9
Q

What is main memory?

A

A contiguous block of read write randomly accessible storage locations.

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10
Q

What can be said about each individual memory location?

A

Can remember one binary word. It can change the word if it receives a write request. It has a unique integer address. It can provide a copy of its contents when a read request is given.

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11
Q

What two facts about main memory lead it to being referred to as RAM?

A
  • It is volatile.

- The contents are not restored when powered up again instead each location has a random pattern of bits.

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12
Q

What does RAM stand for?

A

Random access memory

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13
Q

What are i/o controllers?

A

It is an internal component that allows the processor to interact with a peripheral device through an i/o port.

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14
Q

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

A

Harvard architecture has a separate ram for the instructions and the data whereas Von Neumann uses the same architecture.

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15
Q

Where is Von Neumann architecture used?

A

General purpose computing systems.

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16
Q

When is Harvard architecture used?

A

Embedded systems such as digital signal processing.

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17
Q

What are the two addressing modes?

A

immediate or direct.

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18
Q

What is immediate addressing?

A

When the operand value in an instruction is the actual data.

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19
Q

What is directional addressing?

A

When the operand value in an instruction contains the memory location of the data.

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20
Q

What is the stored program concept?

A

Machine code instructions are stored in main memory. They are fetched and executed serially by a processor that performs arithmetic and logical operations.

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21
Q

State the main components of a processor.

A

Arithmetic logic unit, control unit, clock, general purpose registers, program counter, current instruction register, memory address register, memory buffer register and the status register.

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22
Q

What is the arithmetic logic unit?

A

A unit that performs arithmetic ie division multiplication addition subtraction. It also performs logic ie simple logic circuits such as AND or XOR.

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23
Q

What is a control unit?

A

The component that controls how data moves around the cpu and memory.

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24
Q

What is the clock?

A

It is a pulse measured in hertz that repeatedly switches between 1 and 0. The cpu uses the clock to decided how fast to work.

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25
Q

What are the general purpose registers?

A

Registers inside the CPU that can be used to store general information currently required.

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26
Q

What is the program counter?

A

A store for the address of the next instruction.

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27
Q

What is the current instruction register?

A

A store for the instruction that is currently being decoded and executed.

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28
Q

What is the memory address register?

A

Stores the address of the data that is going to be fetched/read/sent/written to the memory address stored.

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29
Q

What is the memory buffer register?

A

Stores the data that is to be sent/written/was fetched from memory.

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30
Q

What is a status register?

A

A collection of flags that can be used by the cpu to know the current state of the program being executed.

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31
Q

What happens during the fetch stage of the the fetch decode execute cycle?

A

The value in the program counter is copied to the memory address register. The memory address register then send the address in it to main memory. When main memory receives a signal from the control unit via the control bus. It sends the information to the memory buffer register via the data bus. The instruction then moves into the current instruction register and the program counter adds 1.

32
Q

What happens during the decode stage of the fetchdecode execute cycle?

A

The instruction in the current instruction register is decided by the decode unit. (A component connected to the current instruction register.)

33
Q

What happens during the execute stage of the fetchdecode execute cycle?

A

The instruction is executed.

34
Q

What is the processor instruction set?

A

A processor instruction set is the list of instructions that a processor contains and is capable of following. An instruction is specific to each processor.

35
Q

What is an instruction made from?

A

An opcode and an operand.

36
Q

What is an opcode?

A

The part of the instruction that states that action that needs to be completed. The last bit of it provides the addressing mode. The rest are called the basic machine operation.

37
Q

What is an operand?

A

The part of an instruction that provides the data or the address of the data that the instruction is to be performed on.

38
Q

Do you understand assembly code?

A

If not go learn it.

39
Q

What is an interrupt?

A

An interrupt is from some device/source seeking the attention of the processor.

40
Q

What are some of the sources of an interrupt?

A

Hardware failures such as a power failure, program problems such as division by zero or arithmetic overflow, a timer ie a real time clock ensuring the processor performs some tasks at regular intervals. Finally i/o devices.

41
Q

What is an interrupt service routine?

A

A small piece of program code written to process the interrupt event such as a key on a keyboard being pressed.

42
Q

How is information stored about the happenings of the processor before an interrupt?

A

The program counter and all the relevant information is placed onto a stack. If another interrupt service routine comes along the isr with the lower priority is placed onto the stack. The stack is then popped one at a time.

43
Q

Why is saving a processor when an interrupt occurs important?

A

Since the processor is volatile it would be impossible to get that data back.

44
Q

What would be the effect of the processor performance if multiple cores were added?

A

It would allow multiple tasks to be done simultaneously improving performance.

45
Q

What would be the effect of the processor performance if more cache memory was added?

A

It will reduce the average time taken to get information from main memory increasing performance

46
Q

What would be the effect of the processor performance if the clock speed was increased?

A

It would increase the number of cycles per second performed by a computer increasing performance. (Although beyond a point the computer may catch fire so it doesn’t matter.)

47
Q

What would be the effect of the processor performance if the word length was increased?

A

It will increase performance as fewer instructions are required to execute the same amount of information.

48
Q

What would be the effect of the processor performance if the width of the address bus was increased?

A

It would allow more memory words to be addressed.

49
Q

What would be the effect of the processor performance if the width of the data bus was increased?

A

It increases the number of bits that can be transferred per second improving memory.

50
Q

What are two types of barcode?

A

1D and 2D

51
Q

What do barcodes represent?

A

The white portions represent 1s and the dark portions represent 0s

52
Q

How does a bar code reader work out the angle and distance of the bar code?

A

They have guard cells that they use to work out the dimensions of the bar code.

53
Q

How does the reader know if the bar code is upside down?

A

Each section corresponding to a number on the left half has an odd parity and it has an even parity on the right hand side.

54
Q

What error checking is available on barcodes?

A

Check digits and parity bits.

55
Q

What are the differences between 1D and 2D barcodes?

A

2D barcodes have far more space available to them and have the capacity to be read by cameras making them more applicable to everyday users.

56
Q

What are the parts of a barcode reader?

A

A laser, a lens, a mirror and photodiodes.

57
Q

How does a barcode reader read a barcode?

A

The mirror directs the lasers light onto the barcode. The light reflected of the barcode through the lens and hits the photodiode which turns the light into an electrical signal. This then gets converted into digital data.

58
Q

What does a barcode reader do if it fails to read the barcode?

A

It scans the barcode again. It can do this 1000s of times a second.

59
Q

What are the parts of a digital camera?

A

A lens, a sensor and a shutter.

60
Q

What are the two most common types of sensor?

A

CMOS and CCD

61
Q

What does CMOS stand for?

A

Complimentary metal oxide semiconductor

62
Q

What does CCD stand for?

A

Charge coupled device

63
Q

What does the shutter do in a digital camera?

A

It regulates the amount of light entering a digital camera.

64
Q

What does a sensor in a digital camera do?

A

They convert incident light into an electrical charge. The amount of charge in each cell is then measured and converted into a digital signal.

65
Q

How do coloured cameras measure light?

A

They have multiple cells for each pixel. Each cell is filtered so it only accepts one kind of light. These cells are then compared to produce a coloured image.

66
Q

What kind of filter do digital cameras often use?

A

They use a bayer filter. This has two green, one red and one blue filter per pixel and represents the fact that the human eye is more sensitive to green light.

67
Q

What are the parts of a laser printer?

A

A laser, a mirror, a drum, a toner hopper, fusers and a control unit.

68
Q

What is the printing process?

A
  1. The drum is covered with negative electricity
  2. The laser his the drum via the mirror creating neutral spaces on the drum
  3. The toner is stirred in such a way it becomes negative and then it is released from the hopper onto the drum filling only the neutral spaces
  4. A piece of paper is charged positively
  5. The drum rolls past the paper and the toner is attracted to the page.
  6. Fusers then heat the page to bind the toner with the page
69
Q

What four different colours do printers use?

A

Cyan, Yellow, Magenta and Black. (CYMK)

70
Q

What does RFID stand for?

A

Radio frequency identification.

71
Q

Where is RFID used?

A

Oyster cards, contactless bank cards.

72
Q

What are the parts to RFID?

A

a tag and a reader. The tag contains a chip attached to an antenna by a coil of wire.

73
Q

What is inside an RFID chip?

A

A small amount of memory.

74
Q

What are the two types of RFID?

A

Active and passive

75
Q

What is the difference between active and passive RFID tags?

A

Active RFID has a small battery which it uses to constantly emit a signal allowing it to be used from much further distances than passive RFID.

76
Q

How is an RFID tag scanned?

A

The reader emits radio waves which are picked up by the tags antenna. This provides the chip with enough power to use its antenna to send back a radio wave which contains the information held on the chip. This information is then decoded by the reader.

a-level computer science (2 decks)

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