Computer Science IGCSE

• Any form of data needs to be converted into binary format so that it can be processed by the computer
• BINARY NUMBER SYSTEM : the basic building block in all computers -> because it only has 1s and 0s
• A switch in the ON position is represented by 1
• Denary number system : counts in multiples of 10
• A base 10 number system : Denary
• The binary number system : base 2 number system
• Hexadecimal is a base 16 system
• Hexadecimal digit : 1, 16,256,4096
• A computer can only work with binary data
• Computer Scientists find hexadecimal to be more convenient than binary because it is easier to remember and write -> one hex digit represents four binary digits.
• There are four uses of the hexadecimal system -> error codes, MAC addresses, IP addresses, HTML colour codes
• Error codes : shown as hexadecimal values which refer to the memory location of the error
• Media Access Control address : a number which uniquely identifies a device on a network -> refers to the network interface card
• Internet Protocol addresses : An address that is given to each device connected to a network
• HyperText Mark-Up Language colour codes : used when writing and developing web pages, it is used to specify the colour of text, background, and other elements
• A mark-up language is used in the processing, definition and presentation of text, graphics, and other data.
• The ASCII code system : American Standard Code for Information Interchange -> set up in 1963 for use in communication and computer systems -> newer version of the code published in 1986
• The standard ASCII code character set consists of 7-bit codes that represent the letters, numbers and characters found on a standard keyboard
• Soundwaves are vibrations in the air -> the human ear senses these vibrations and interprets them as sound
• Each sound wave has a frequency, wavelength and amplitude
• The amplitude specifies the loudness of the sound
• Sound waves vary continuously -> sound is analogue and computers cannot work with that data -> they then need to be sampled in order to be stored in a computer
• Sampling : measuring the amplitude of the sound wave -> done using an analogue to digital converter
• To convert the analogue data to digital -> the sound waves are sampled at regular time intervals
• 4 binary bits can be used to represent each amplitude value -> increasing the number of possible values used to represent sound amplitude also increases the accuracy of the sampled sound (ex : using a range of 0 to 127 instead of 0 to 10 )
• Sampling resolution : the number of bits per sample
• Sampling rate : the number of sound samples taken per second -> measured in Hertz
• Using a higher sampling rate or larger resolution -> result in a more faithful representation of the original sound source and a greater file size
• Benefits of using a larger sampling resolution -> larger dynamic range, better sound quality, less sound distortion
• Drawbacks of using a larger sampling resolution -> produces larger file size , takes longer time to transmit or download music files, requires greater processing power
• Bitmap images are made up of pixels (picture elements)
• Colour depth : the number of bits used to represent each colour
• Image resolution : the number of pixels that make up an image
• A bit is the basic unit of all computing memory storage terms
• The byte is the smallest unit of memory in a computer
• 1 byte is 8 bits
• Necessary to reduce or compress the size of a file as sound and image files can be very large
• Reasons to compress the size of a file

  1. to save storage space on devices, reduce time taken to stream or upload and reduce costs
• Lossy file compression : the original file cannot be reconstructed once it has been compressed
• When applying a lossy file compression algorithm to an image, it may reduce the resolution and or the bit and colour depth