Data Representation (PAPER 1) Flashcards by Yuvraj Gakhar

What is a bit
- What two characters represent bits
- What do each of these two show
- What does bit stand for

the smallest measurement of data
- 1 and 0
- 1 shows electricity is flowing, 0 shows it is not flowing

Binary digit

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What are the 8 commonly used units of data
- how do their sizes compare
- What are their symbols

Bit - b
Nibble - 4 bits
Byte - B - 8 bits
Kilobyte - kB - 1000 / 1024 bytes
Megabyte - MB - 1000 / 1024 Kilobytes
Gigabyte - GB - 1000 / 1024 Megabytes
Terabyte - TB - 1000 / 1024 Gigabytes
Petabyte - PB - 1000 / 1024 Terabytes

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How many values can a nibble take
- How many can a byte take

Nibble - 2^4 = 16 values
Byte - 2^8 = 256 values

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What are the binary and hexadecimal numbers from 0 - 15

D = B = H

0 = 0 = 0
1 = 1 = 1
2 = 10 = 2
3 = 11 = 3
4 = 100 = 4
5 = 101 = 5
6 = 110 = 6
7 = 111 = 7
8 = 1000 = 8
9 = 1001 = 9
10 = 1010 = A
11 = 1011 = B
12 = 1100 = C
13 = 1101 = D
14 = 1110 = E
15 = 1111 = F

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Which bit has the largest value
- which has the least value

The left most bit
- the right most bit

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What is the value 00110101 in denary

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What is the value 79 in binary

01001111

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What is 10001101 + 0100100 (binary)

11010101

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What is an overflow error

When a number has too many bits - a result requires more bits than the CPU is expecting

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Which bit will be the first to overflow
- Where will these extra bits be stored
- What is used to show that an overflow error has occured

The left most bit - most significant
Elsewhere
Overflow flags

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Add the binary numbers below, giving the answer as an 8-BIT BINARY NUMBER

11010001 + 10010100

101100101

REMOVE THE LEFT MOST BIT

01100101

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What is a binary shift
- What happens when a binary number is multiplied by 2, what can it cause
- What happens when a binary number is divided by 2, what can it cause

When every bit in a binary number is moved left or right by a certain number of places
- left shift by 1 place, can cause overflow errors
- right shift by 1 place, can cause bits to ‘drop off’

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What identifies how many places a bit moves during a binary shift

The power of 2 that a number is being divided / multiplied by

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multiply 00101001 by 8

8 = 2^3
3 place shift to the left

001,01001000 ; [001] will overflow

01001000

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divide 00111100 by 4

4 = 2^2
2 place shift to the right

00001111,00 ; [00] will drop off

00001111

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What is the alternative name for hexadecimal

Base - 16

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What denary numbers can a single hex character represent
- How many bits equate to a single hex character

0 - 15
- 4 bits (a nibble)

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What is the hex number 87 in denary

135

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What is the denary number 106 in hexadecimal

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Why do programmers prefer using hex when coding

easier to remember large numbers
less chance of input errors
easier to convert between binary and hex than binary and denary

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What does moving left one space do to the place values in hex

multiply by 16

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What are the steps to converting a binary number to hex

split binary number into nibbles
convert each nibble to hex

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What is 10111001 in hexadecimal

What is 111110 in hexadecimal

What is 8C (hex) into binary

10001100

What is a character set

a collection of characters that a computer recognises from their binary representation

How does pressing a button on a keyboard translate to a character on a computer

pressing the button gives a binary signal to the computer saying which key is pressed - computer then uses character set to translate the binary code into a character

What are the two most common character sets - How many bits are used for each - What characters are able to be represented by each

- ASCII and Unicode - 7 bits for ASCII, with an extra 0 at the front to make it one byte, Multiple bytes per character for Unicode - ASCII represents all English letters, numbers, symbols and commands Unicode aims to store every single possible character including different alphabets (Greek, Russian etc. )

What is the formula for file size of a text file

file size (bits) = number of bits per character x number of characters

How are images made / stored

as a series of pixels (bitmap)

How are colours within a image represented

as a binary code

how many bits are required for each pixel for a black and white image

1 bit - 0 for white and 1 for black

How can a greater range of colours be available in an image

by increasing the number of bits for each pixel

What is the colour depth

the number of bits used for each pixel

How can you work out the amount of colours available from the colour depth

total number of colours = 2^ colour depth

how many colours are available for a - 1 bit image - 4 bit image - 6 bit image

- 2^1 = 2 - 2^4 = 16 - 2^6 = 64

What colour depth do most modern devices use - how many colours are available - how are they split among red, green and blue

24 bit colour depth - 16 777 216 colours - 8 bits each for red, green and blue

What is the image resolution What is the formula for image resolution

the number of pixels in the image - width x height

What is the formula for the file size of an image

file size (bits) = image resolution x colour depth

What is the file size in MB of an 8 bit image that is 2000 pixels wide and 1000 pixels high

2000 x 1000 x 8 = 2000000 x 8 = 16000000 16000000 / 8 = 2000000 bytes 2000000 / 1000 = 2000 KB 2000 / 1000 = 2MB

What is metadata - what does it include

The information stored in an image file which helps the computer recreate the image - file format, height, width, colour depth - can also include date and time of creation or last edit

How is sound recorded by a microphone

as analogue signals

What are analogue signals

pieces of continually changing data

What must happen to analogue signals before they can be read by a computer - what technology is required for this - what is this process called

it must be converted into digital data - analogue to digital converters - sampling

How is an analogue signal converted to digital data

- samples are taken of the signal at regular intervals - the curve is created digitally (looks similar to bar graph)

What is the issue with digital data - how can this be improved

- it isn't continuous - lots of data gets lost - by taking samples more often

What is the sample rate - what is it measured in

the amount of samples taken per second - Hz (Hertz) / KHz (Kilohertz)

What is Bit Depth

the number of bits available for each sample

What is the formula for bit rate

sample rate x bit depth

What is the formula for file size of a sound file

file size (bits) = sample rate (Hz) x bit depth x length (s)

How does increasing the sample rate affect the sampled sound

it will be better quality and a closer match to the original recording

How does increasing the bit depth affect the sampled sound

the file will pick up quieter sounds resulting in a sampled sound closer to the original recording

What is data compression - Why is it used (4)

When file sizes are made smaller while trying to make the compressed file as true to the original as possible - take up less storage space - streaming / downloading is quicker as less bandwidth is used - web pages load more quickly - email services normally have restrictions on sizes of attachments

What are the two types of compression - how do they work

Lossy - permanently removes data from the file Lossless - temporarily removes the file while storing and restores it to its original state when opened

What are the pros and cons of lossy compression

P - greatly reduced file size, less bandwidth to download, can be read by lots of software C - loses data permanently, can't be used on software or text files, worse quality

What are the pros and cons of lossless compression

P - data is only temporarily lost, can be decompressed, can be used on text and software files C - only a slight reduction in file size