Data Representation GCSE 9-1 COMPUTER SCIENCE
first 4 powers of 16
16^0=1 16^1=16 16^2=256 16^3=4096 16^4=65536
why dont people just use denary instead of hex?
bcoz it is easy to convert between hex and binary!
Why use binary (only 1 and 0)?
because a cpu is made of millions of transistors (tiny electronic switches) that can be in one of the two states (on or off). So 1 represents true and 0 represents off
Why was a seven bit ASCII character set changed to a byte? this is called extended ascii code
because as 8 bit machines became more standard, the ASCII character set made use of the extra bit (providing a further 128 characters) SO CONVENIENTLY A BYTE IS USED TO REPRESENT ALL CHARACTERS FOR THE ENGLISH LANGUAGE
Why do we say base 2 ?
because there is only 2 possibilities we say that this is a base 2 number system
how many decimal number (base 10) will a nibble cover?
between 0 and 15
base 2
binary
What is binary?
binary is a number system made up of only 1 or 0
what would be a sensible unit for the size of a person's surname?
bytes
what is one piece of text known as?
character
what is character set?
character set is a symbol on a computer keyword that can represent as a code in binary
what is bit depth also known as?
colour depth
base 10
denary
What happens with higher bit/colour depth?
greater ranger of colour and better quality but lots of storage required
nibble
group of 4 bits and its half a byte
What are hexadecimal numbers?
hexadecimals use the base 16 number system. It has 16 possibilities from 0-9 and then A-F (that represent values of 10-15)
What happens with greater number of dots per inch (pixels)
higher the quality, larger the file size as it holds more pixels and data
what is colour depth
how many bits needed to represent number of colours . BASICALLY -colour depth refers to the amount of data that can be used to indicate the colour of each dot or pixel on your display
TRUE OR FALSE? Computers use the binary number system to represent data
true
TRUE OR FALSE? IMAGES ARE REPRESENTED IN BINARY?
true
TRUE OR FALSE? hexadecimal number system has place values which increase by the power of 16
true
TRUE OR FALSE? more colour= more bits= more memory needed
true
TRUE OR FALSE? when uncompressed, no data is lost
true
TRUE OR FALSE? with bigger colour depth = more colours to choose from
true
using 8-bit ascii code, what would be the total size in bytes of the word "Computer Science"?
16 bytes in total (also count the spaces)
how many bits does Unicode use to represent every character in various languages around the world?
16 or 32 (2 sets of 16 bits) bits
how many numbers can be represented with 4 bits?
16 possibilities (from 0-15)
how many colours with 4 bit
16 possible colours
how many colours with 24 bit colour depth (true colour)?
16,777,216 possible colours (256 (Red) X 256(Green) X 256 (blue))
Hexadecimal number AF in denary?
175
Hexadecimal B2 in denary?
178
How is resolution written as? E.g 1080 pixels width and 1920 pixels length
1920 x 1080 (DO NOT MULTIPLY THEM)
in what year did american standard association agreed on a set of codes to represent the main characters in the English language?
1960
Convert this binary 0001 1111 in hex?
1F
how many colours in one bit image?
2 colours (white and black) so each pixel is represent by one bite (0 or 1) of memory
ascii character set can hold up to how many characters?
256
how much can a byte store?
256 different numbers (0-255)
Total number in 8 digit
256 possibilities (0-255)
how many colours with 8 bit colour depth
256 possible
how many colours in 8-bit?
256, so each pixel will be represented by eight bits of memory (so for example colour yellow is 10100011 (for instance))
tell the first 10 digits of powers of 2
2^0= 1 2^1 =2 2^2=4 2^3=8 2^4=16 2^5=32 2^6=64 2^7=128 2^8=256 2^9=512 2^10=1024
which one is black and white? 1 or 0?
BLACK = 1 WHITE = 0
why do data such as images and text need to be converted to numbers?
Because computer system can only deal with 0 and 1
Hexadecimal F in binary and denary?
Binary = 1111 denary = 15
What is the issue that computer scientists are trying to solve by using hexadecimal numbers?
Quickly small binary numbers can become very long like 8 or 9 digits. By using hexadecimal numbers we are solving and dealing with this issue without the long string of digits.
DID YOU KNOW? higher bit rate (data per sec) = higher quality or high colour depth
WOW!
What is metadata (data about data)?
a set of data that describes and gives information about other data. for a computer to interpret the numbers (binary as the images are stored as) to produce the image. It need to be told: -height and width (in pixels) -colour depth -author
What is compression?
is a technique where we reduce file size while maintaning quality or original data
what is bitmap/bitmap images?
are made up of rows of 'dots' called 'pixels'
What is check digit?
is an additional digit at the end of a string of other numbers designed to check for mistakes in input or transmission.
disadvantage of unicode
as it is larger than ascii becos it uses between 16 and 32 bits per character, it takes up more storage space when saving documents
what is 10000101 in denary?
133
Hexadecimal: E
14
Hexadecimal: F
15
rules of adding binary?
- 0+0=0 - 1+0= 1 - 1+1=10 (1 is the carry) - 1+1+1=11 - 1+1+1+1=100 (double carry)
What could 1 gigabyte hold?
-3,000 books and 25% of a typical movie
image file types
-BMP -JPG -GIF -PNG -TIF
Why use hexidecimal number?
-binary produces long strings and can be difficult to work with. hex is shorter -hex can be easily converted to/from binary as there is 1 hex digit per nibble -hex is less likely to error
why use compression?
-download times are reduced -data allowances go further -voice can be transmitted fast enough to keep up with speech
Why use symbols in hexadecimal?
-easier/shorter to read -because the second column is 16, we have to count to 15 before moving or placing a 1 in the 16s column. But in all number system, placing two difits in one column is not allowed therefore we use symbols to represent 11,12,13,14 and 15
Is zipping lossy or lossless compresion?
-lossless
What are the two types of compression?
-lossy and lossless
what are the two ways of improving image?
-more pixels in a compact space -or more vibrate colours
What can petabyte store?
-over 2,000 years worth of songs -315 million photos (3MB each)
What can a terabyte store?
-over 300 hours of video -1,000 copies of encyclopaedia britannica
Tell me 3 facts about lossy compression?
-permanently removes some data -recreates the file using the remaining data and uses algorithms to guess the removed content
benefits of compression?
-smaller file = fewer packets = faster transmission time -reduces download times of video, sound and image files -speeds up transmission of webpages that use images -reduces space on disk/servers -enables better streaming of music and video
Tell me 4 facts about lossless compression?
-uses algorithms to recognise patterns in data -patterns are recorded in a sequence -this pattern is used to specify what a file should represent (in terms of bits) -the pattern is used to build the original file back
what happens each time you hit a key on keyboard?
1. computer generates a code for that letter 2. then it is processed by the cpu 3. the result might be the letter appearing on the screen or printed on paper
how does binary work?
1. computer programs are set of instructions 2. each instruction is translated into machine code -simple binary codes that activate the cpu 4. programmers write computer code and this is converted by a translator into binary instructions that the processed can execute
Hexadecimal: A
10
1 terabyte (TB)
1000 gigabytes (8bits (1024 to be exact)) or 1 trillion bytes
1 megabyte (MB)
1000 kilobytes (8 bits (1024 to be exact)) and roughly 1 million bytes
1 gigabyte (GB)
1000 megabytes (8 bits (1024 to be exact) or 1 billion bytes
1 petabyte (PB)
1000 terabytes (1024 to be exact) 1 quadrillion bytes
binary shift dividing = 216 to 1 place to right
108= 01101100
Hexadecimal: B
11
what is 202 in binary?
11001010
Hexadecimal: C
12
how many different codes does ASCII require?
127
how many codes does English language require?
127 in total - 7 digit binary -26 letter of the alphabet in upper case -26 letter of alphabet in lower -10 numeric symbols -32 codes reserved for non-printable control codes
Hexadecimal: D
13
Binary shift multiplying = 27 to 1 place
54 = 110110
how many character can be represented with 16 bit Unicode character set?
65,536
how many bits does ASCII require?
7 bits because in binary 127 is 1111111
convert 1001 1100 in hex?
9C
advantages and disad of lossy image compression?
Advantages are much smaller file size and disadvantges are some loss of quality and removes data permantly
What does ASCII stand for?
American standard code for information interchange
What wrong with the word "bytes"
Bytes is always written with a capital B
Convert this binary 1101 1101in hex?
DD
What is the difference between GB and Gb
GB is used for gigabytes and Gb is used for gigabit -1GB = 8Gb -1MB = 8Mb -1 TB = 8Tb
printed book and other products have a unique barcode with a isbn or ean, what do they both stand for?
ISBN- INTERNATIONAL STANDARD BOOK NUMBER EAN- EUROPEAN ARTICLE NUMBER
What is an overflow?
It occurs when doing binary addition when the answer is 9-bit in lenght
Give example of lossy compression
JPG, GIF, MP3
what would be a sensible unit to store document file sizes
Kilobytes (KB)
What is lossless compression?
Lossless compression is a class of data compression algorithms that allows the original data to be perfectly reconstructed from the compressed data.
Would lossy sompression work for computer programs?
No, because you would be removing actual data and instructions
Give example of lossless compression
PNG, TIFF
How does lossy compresion works?
SIMILARLY coloured pixels are all made the same.
TRUE OR FALSE? keyboard characters generally take up 1 byte (8 bits) of storage
TRUE
TRUE OR FALSE? we often use GB to refer to hard drives sizes
TRUE
TRUE OR FALSE?.24 bits can represent 16.7 million colours
TRUE
TRUE OR FASLE? MORE BITS = MORE COLOURS
TRUE, BUT LOTS OF SPACE needed and good display is needed (eg crappy tv will try it best to blend those colours to the original image however it will just seem a little block)
TRUE OR FALSE? Within the Unicode system, the original ascii codes are the same and still available
TRUE, other codes have just been added on alongside the original
TRUE OR FALSE? Byte is a building block for every other measurement
TRUE... Every other storage measurement is made up from multiples of byte
What can be calculated using modulo 10?
The first 12 digits of the barcode are the unique item and the 13th is the check digit?
TRUE OR FALSE? -uncompressed data is not the same as the original
True
To solve the issue with ascii character set, what was the name of the new character set?
Unicode, as computer developed and 16 bit computer were introduced, Unicode was developed to accommodate the various other languages in the world
Byte
a group of 8 bits
monochrome meaning
a image is only in black or white (1bit = 1 or 0)
why is it easy to convert from hex to binary?
all you have to do is split binary byte into 2 nibbles and the left nibble is ur left hex number and right nibble is your right hex number
what is resolution?
amount of pixels across x amount of pixels down
1 kilobyte (KB)
another common unit of measurements. 1000 byte in a KB (1024 to be exact)
how can we improve the quality of the image in terms of 'how defined' the image is?
answer is pack more pixels into the same space making the image appear 'less blocky' or 'pixelated'
how to improve quality of image in terms of it depth in colour
answer is that we have more colours to choose from for each pixel. the greater range of colours makes image look 'real'
What would be a sensible unit for a music file?
megabytes
What happens with more colours
more real the image looks but bigger the file size as each pixel is generated from a larger binary number, therefore more data
binary shift- divide
right shift
Bit
short for Binary digit: Smallest unit of data a computer can store. Only stores 0 (fasle) or 1 (true)
why is it important that there is an agreed set of codes for characters?
so that all computers systems behave in a similar way - standard ensures that different devices (which might be manufactured by differing companies) can communicate to each other with the same character-code.
What do units describe + put them in order
the following units describe how much disk space capacity or data storage is used: -bit -nibble -byte -kilobyte -megabyte -gigabyte -terabyte -petabyte
problem with ascii?
the issue is that with some languages such as chinese or japanese is that they use thousands of different characters which cannot fit into a byte.
denary numbers
the numbers human work with. also known as base 10
ENCODING
these binary numbers are converted (encoded) in different DATA formats to give them meaning -audio can be encoded as audio file (mp3 or wav -video as video file formats such as mpeg4 or h264 -text as in character set eg unicode or ascii -images are file format like PNG or JPEG
Higher DPI = higher revolution = more accurate and defined image! Give one disadvantage of this
this means more dots/pixel, meaning more bits therefore more data needed to store meaning bigger file size
What can Megabytes be used to measure?
to measure transmission speeds on the web and also storage space on a CD
binary shift- multiply
to the left
what is 24 bit display also known as?
true colour display
TRUE OR FALSE? higher number of colours that a pixel could be means higher colour depth/better quality which in turn means a more real looking image
true, but also more data is needed therefore increasing the file size (ram)
true or false? all data that it needs to work with like numbers, sound and images must be converted into binary for the computer to be able to process it
true, it is exactly the same for text
TRUE OR FALSE? Each pixel is represented by a binary number
true, so behind the scenes a picture or an image is in fact a series of numbers
where is compression mostly used?
used with sound, image and video file types
when is nibble most useful?
when converting between binary and hexadecimal
