Topic 2 data

• Binary

  Computers only understand 2 states: on and off (0 or 1)

  This is represented by switches, and computers are essentially calculators made up of billions of switches.

  Everything needs to be converted to binary for a computer to process
• 1 byte has 8 bits and a nibble is 4 bits
• 2^n shows how many unique binary patterns can be generated where n is the amount of bits
• signed intergers use the MSB ( most significant bit) to represent whether the number is negative or positive
• If the MSB is 1, the number is negative. If the MSB is 0, the number is positive
• Two's complement is a way to show negative numbers. To make a positive number negative, flip the bits and add 1
• a binary shift to the left multiplies the number by 2, a binary shift to the right divides by 2.
• A logical shift replaces all the empty spaces with a 0
• An arithmetic shift replaces all the empty spaces with the MSB
• logical - unsigned integers
• arithmetic - signed and two's complement integers
• an overflow error is when an operation produces a result that requires more bits to store than available
• Consequences of overflow errors are: The program crashing or producing unreliable or incorrect results.
• hexadecimal is a base 16 number system that has 16 unique digits. 0 to 9 and A to F
• b = bits

  B = bytes (8 bits)

  KB = kilobytes (1000 bytes)

  MB = megabytes (1000 kilobytes)

  GB = gigabytes (1000 megabytes)

  TB = terabytes (1000 gigabytes)
• B = bytes (8 bits)

  KiB = kibibytes (1024 bytes)

  MiB = mebibytes ( 1024 kibibytes)

  GiB = gibibytes (1024 mebibytes)

  TiB = tebibytes ( 1024 gibibytes)
• there are 3 main datatypes = string, integer and float.
• a string is a combination of text, number and symbols
• an integer is a whole number
• a float is a number with a decimal point
• a character set is a set of letters, symbols and digits that are all represented by its own binary code.
• ASCII = american standard code for information interchange. Its a 7 bit code that can represent 128 different characters.
• Extended ASCII = has 8 bits so 256 unique characters.
• Bitmap images are made of pixels.
• a pixel is the smallest identifiable area of an image. each pixel is a single colour and is given a binary value that represents the colour.
• colour depth is the number of bits used to encode the colour of each pixel 8 bits = 256 colours
• image size = width x height
• resolution is the number of pixels per inch of the displayed image
• file size = width x height x colour depth
• analogue sounds = sound caused by vibrations travelling through a medium such as air or water
• sound sampling is when samples of sound are taken at regular fixed intervals
• sample rate = number of samples per second, measured in Hz
• bit depth = number of bits used to encode each sample
• audio file size = sample rate x bit depth x recording length
• data compression = reduces the size of a file
• lossy compression -some of the data is permenantly lost , but enough remains so the file is useful.
• lossless compression = none of the original data is lost, and it can be perfectly restored