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AS COMPUTING > Comp1-Data rep > Flashcards

Comp1-Data rep Flashcards

1
Q

Convert a negative denary number to twos complement.

A
  1. Find the binary value for the positive number.
  2. Flip all the digits.
  3. Add 1 to the result (actually add 1 with binary addition)
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2
Q

Convert a negative twos complement to denary? 2 methods

A
  1. Flip the bits. Add one . work out denary.

2. using the place values and adding these up.

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3
Q

In binary subtracting do…..

A

turn the number being subtracted into a twos complement

add this.

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4
Q

Why is hex used?

A

as a short hand notation for binary, so we can read and write it more easily.

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5
Q

Whats the most significant bit?

A

The leftmost bit. (highest value)

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6
Q

what is the least significant bit?

A

The rightmost bit. (lowest value)

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7
Q

COnvert denary to hex?

A

convert to binary.
divide into groups of 4, starting from the right.
convert each group of 4 into hex.

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8
Q

What is the range of sybols in hex. (what is 15 and 0 in hex?)

A

0-9 then A-F (with F=15, 0=0)

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9
Q

how do fixed point binary number work.

A

the decimal is in a set place. to the left the place values increase normal.
to the right they start with 1/2 , 1/4 , 1/8 so on.

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10
Q

How many characters are in ASCII, how many bits is this?

A

128, 7 bits.

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11
Q

What is A in ASCII?

A

65 (the next 26 are the other capitals)

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12
Q

What is a in ASCII?

A

97 (the lower case is the uppercase +32)

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13
Q

whats the eight bit in ASCII used for?

A

Error checking.

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14
Q

how many bits does UniCODe use?

A

16 bits ( the first 128 are the same as ASCII)

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15
Q

How does a single parity bit work?

A

its set so either the total number of 1s = odd or even, this then gets checked to see if it matches.
This can detect a odd number of mistakes.

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16
Q

What is majority vote? And is it any good?

A

sending the same data 3 times and usung the most common bit value(for that specific bit) to represent that bit.
This is very expensive as three times the data has to been sent.

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17
Q

How does hamming code work.(the pairty bits)

A

The 1,2,4,8,16….. bit are used as parity bits
position one checks odd numbered bits and is set so they’re even
Bit 2 checks alternate pairs eg 2,3..6,7..10,11
Bit 4 checks alternate quads eg 4,5,6,7..12,13,14,15
Bit 8 checks alternate 8s

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18
Q

how do you correct an error with hamming code?

A

check the parity bits, fine all the wrong ones. add up their values, this will be the location of the incorrect bit.

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19
Q

Why is hamming code still used?

A

provides a good balance between error detection and correction - Used in wireless communication.

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20
Q

What is gray code?

A

A binary representation where two consecutive values differ in only one bit.

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21
Q

What is the full name for gray code?

A

Binary reflected gray code.

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22
Q

Why is gray code popular?

A

it prevents some data errors that can occur during state changes in slower systems to improve reliability.
Used in counters as only one bit has to change at once and this reduces energy used.

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23
Q

When is gay code used.

A

In angular movement systems. The reader may store halfway between two values and read both, however since they only differ by 1 bit the value read is guaranteed to be one of the two.

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24
Q

How do you convert binary to gray code?

A

Start at the rightmost bit, if the bit to the left is a one invert it. leave the leftmost bit unchanged.
1000–>1100, and 1010–>1111

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25
Q

What is a pixel?

A

the smallest addressable area or smallest solid block of colour in a image.

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26
Q

What is a bitmap?

A

created when the pixels of an image are mapped to positions in memory that store binary codes representing the colour of each image.

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27
Q

what si the Resolution of a VDU

A

a quantity expressed as the number of pixels per row by the pixels per collumn.

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28
Q

What is the resolution of a image?

A

the number of dots(pixels) per inch or centimeter.

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29
Q

What determines picture sharpness?

A

the size of the pixels.

30
Q

What happened to enlarged bitmaps?

A

the pixels get bigger and the picture becomes fuzzy.

31
Q

What is colour depth?

A

the number of bits used to represent the colour of a single pixel in a bitmapped image.

32
Q

What is 1 bit colour?

A

black and white or monochrome.

33
Q

What is 12 bit direct colour?

A

4 its for R,G and blue giveing 4096 colours. USed in devices with limited colour diplay eq nokia brick.

34
Q

What is true colour?

A

8 bits used for R, G and B giving 16,777,216 colours possible.
Is very close to colours that are found in the real world.

35
Q

what is 32 bit colour?

A

Really true colour. Extra 8 bits are because most processors are 32 bit not 24.
they are used for partial transparency or nothing.

36
Q

What is vector graphics?

A

Dividing a graphic image into objects- lines, arcs, curves, circles, ellipses, rectangles, polygons etc.

37
Q

How are objects drawn in vector graphics.

A

Using drawing commands(properties in a drawing list) such as corner coords, center coords, colour, radius, fill?, fill colour.

38
Q

What is an object?

A

a component of a vector graphic , such as a line, rectangle.

39
Q

What is a drawing list?

A

the list of drawing commands that recreate a vector graphic.

40
Q

what is a property?

A

a property of a vector graphic object describes things such as size, colour, fill, shading, direction, font size etc.

41
Q

What is the staircase effect?

A

When you enlarge a bitmap the pixels get bigger until you can notice them , which is the staircase effect.

42
Q

What happens when you enlarge a vector graphic image?

A

Scaling is applied to endpoits , andsize. which avoid the staircase effects . and the scaling happened geometrically because they deal with objects not pixels.
No distortion.

43
Q

Advantages of vector graphics?

A

Geometric images require fewer bytes of data
geometric images are stored faster and upload/dload to the web faster.
scale without distortion.
You can manipulate the individual objects.

44
Q

Advantages of bitmap graphics?

A

Images that have a continuous areas of colour, such as photos take up fewer bytes.

45
Q

What is data compression?

A

Squeezing data into a fewer number of bytes then before.

46
Q

What is run-length encoding?

A

a simple compression technique, that takes advantage of many pixels in a row being the same colour eg the sky. by storing number of bits then coulour.
Lossless compression.Uused in gif, jpeg, png etc)

47
Q

What is lossy compression?(in pictures?)

A

Disregards information that isnt considered important, eg background scenery is stored at a reduced resolution. and reducing the bits per colour used
The decompressed image is different but good enough for us to not notice.

48
Q

What is analogue data?

A

physical quantities such as temp that vary continuously in the real world.

49
Q

What is digital data?

A

data that takes the form of discrete values.

50
Q

What is a analogue signal?

A

an electrical signal that varies in a continuous manner.

51
Q

How is the sound wave captured in a analogue system?

A

the pressure change is recorded by a transducer (usually a mic), this produces a current/voltage that is proportional to the sound pressure. This can be transmitted by phone/radio. Its reproduced by vibrating a mechanical surface on a loud speaker or equivalent.

52
Q

A more rapid vibration=

A

a higher pitch.

53
Q

What is a pure tone?

A

a regular sine wave (no superposition patterns)

54
Q

How does vinyl work?

A

The long grove is made so its a similar shape to the sound wave. This gets picked up needle, whcih produces electrical signals proportinal to the height change. This is amplified and fed to a loud speaker.

55
Q

Whats the sample speed of a CD

A

44,100 hz in two stereo channels.

56
Q

Sample size for a cd?

A

16 bits

57
Q

What is a tranducer?

A

converts continuous physical things eg pressure to a continually varying electrical signal.
A traducer converts energy from one form to another.

58
Q

What is a digital signal?

A

An electrical signal with voltage changes that are in discrete steps. (o and 5V)

59
Q

What is a ADC and how does it work?

A

Analogue to digital converter.

Sample the analogue signal , convert this(the vertical displacements) to a signal using only 2 values for voltages.

60
Q

Wha is a DAC and how does it work?

A

Digital to analogue converter.

Turns the digital signal of two values back into an analogue signal via their heights.

61
Q

What is PAm?

A

pulse amplitude modulation.
Sampling analogue signals at regular intervals
Producing an electrical pule proportional to the original signal height This is codes as a set number of bits.
IT outputs the least significant bit first (right most)

62
Q

What must sampling rate be?(this is Nyquist’s theorm)

A

at least twice the highest frequency.

63
Q

What is quantisation noise/

A

the difference between the original amplitude and the amplitude of the recreated analogue sound wave (via a DAC)

64
Q

What is MIDI?

A

Musical information digital interface.

A way of representing sound by storing the notes,the instrument and the duration.

65
Q

Why is MIDI useful?

A

compact

can be transposed into a different key easily and its easier to synthesis or change instrument.

66
Q

What is synthesis sound?

A

using digital means to generate audio signals resembling instrumental sounds or the human voice.

67
Q

What is MPEG compression?

A

removing the frequencies that the brain and human ear wont notice. giving about 1/10 the data to be stored to 0.25MB per min. (in MP3)

68
Q

How much does 1 min of sound take up in WAV format?

A

2.5MB

69
Q

How does sound steaming work?

A

the client receives the data and stores t in a buffer until it needs to be used. a few seconds later it starts. (playing from the buffer) if the buffer runs out, the steaming will momentarily pause.

70
Q

Why is sound streaming good?

A

no downloading or storage is needed = good, also in theory it prevents copying.

71
Q

How does editing sound work?

A

when its stored digitally it can be edited to remove notes, background noise etc.

72
Q

Converting sign in binary.

A

leave every bit up to and including the first 1(starting from the right), then flip the rest.

AS COMPUTING (12 decks)

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