Data Representation (PAPER 1) Flashcards
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
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
How many values can a nibble take
- How many can a byte take
Nibble - 2^4 = 16 values
Byte - 2^8 = 256 values
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
Which bit has the largest value
- which has the least value
The left most bit
- the right most bit
What is the value 00110101 in denary
53
What is the value 79 in binary
01001111
What is 10001101 + 0100100 (binary)
11010101
What is an overflow error
When a number has too many bits - a result requires more bits than the CPU is expecting
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
Add the binary numbers below, giving the answer as an 8-BIT BINARY NUMBER
11010001 + 10010100
101100101
REMOVE THE LEFT MOST BIT
01100101
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’
What identifies how many places a bit moves during a binary shift
The power of 2 that a number is being divided / multiplied by
multiply 00101001 by 8
8 = 2^3
3 place shift to the left
001,01001000 ; [001] will overflow
01001000
divide 00111100 by 4
4 = 2^2
2 place shift to the right
00001111,00 ; [00] will drop off
00001111
What is the alternative name for hexadecimal
Base - 16
What denary numbers can a single hex character represent
- How many bits equate to a single hex character
0 - 15
- 4 bits (a nibble)
What is the hex number 87 in denary
135
What is the denary number 106 in hexadecimal
6A
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
What does moving left one space do to the place values in hex
multiply by 16
What are the steps to converting a binary number to hex
- split binary number into nibbles
- convert each nibble to hex
What is 10111001 in hexadecimal
B9
What is 111110 in hexadecimal
3E
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
