Computing Mock Revision

Computing Mock Revision

1. Algorithms

   • Pseudocode
     • INPUT – indicates a user will be inputting something
     • OUTPUT – indicates that an output will appear on the screen
     • WHILE – a loop (iteration that has a condition at the beginning)
     • FOR – a counting loop
     • REPEAT – UNTIL – a loop (iteration) that has a condition at the end
     • IF – THEN – ELSE – a decision (selection) in which a choice is made
   • Flowcharts
     • Start / start
       • Beginning and end points
     • Process
       • An instruction or command
     • Decision
       • A decision, either yes or no
     • Input and output
       • An input is data received, output is a signal or data sent from the computer
   • Definitions
     • An algorithm is a set of instructions
     • A computer program is an implementation of an algorithm and that an algorithm is not a computer program.
     • Decomposition means breaking a problem into a number of sub-problems, so that each subproblem accomplishes an identifiable task, which might itself be further subdivided.
     • Abstraction is removing unnecessary detail from a problem
   • Searching and sorting
     • Searching algorithms
       • Linear search
         • A linear search is a simple, sequential search. It starts at the beginning of the list and moves through the items, one by one, until it finds a matching value or reaches the end without finding one.
       • Binary search
         • The binary search algorithm searches an ordered list to find an item by looking at the middle item (the median) and comparing it with the search value. It works like this:
     • Sorting algorithms
       • Bubble sort
         • This algorithm works by checking if the 1st and 2nd values are in order and orders them if not, then the 2nd and 3rd, 3rd and 4th etc...At the end, the process is repeated from the beginning until the list is in order
       • Merge sort
         • This algorithm works by cutting the list in half and keeps doing so until each part is one, then the list is merged in numerical order

2. Data representation

   • Binary, hex and decimal
     • Binary
       • Base 2
       • Computers represent all data and instructions in binary form
       • Up to 1111 1111
     • Hexidecimal
       • Base 16
       • Used in computer science as it is easier to understand
       • Up to FF
     • Decimal
       • Base 10
       • Used as every-day numbers
       • Up to 255
   • Units of information
     • Sizes
       • b is bit - Either a 0 or 1
       • B is byte - 8 bits
       • kb is kilobytes - 1000 bytes
       • mb is megabytes - 1000 kilobytes
       • gb is gigabytes - 1000 megabytes
       • TB is terabytes - 1000 gigabytes
     • 7- bit ASCII
       • Characters are in groups... A is 65, B is 66... and lower case letters are grouped as well
       • Goes up to 127 / 111 1111
     • Unicode
       • Has many different characters in different languages
       • Unicode uses the same digits as ASCII up to 127
   • Images and sound
     • Representing images
       • Pixel is short for picture element
       • Size of an image is width of image x height of image
       • Colour depth is how many bits used to represent one pixel
       • Size = W*H*D .... Width * Height * Colour depth
     • Representing sound
       • Sample rate is the number of samples taken in a second, measured in hertz
       • Sample resolution is the amount of bits per sample
       • File size = sample rate * sample resolution * seconds
   • Data compression
     • Huffman encoding
       • Data is put in order for how many times it appears and then the lowest two are put together and rearranged with the new size value. This process repeats until there is one long dtata tree
     • Run length encoding
       • Saves the data as each value and the number of times is appears
         • 1,2,2,2,4,4,5,6,7,7,7,7
           • (1,1),(3,2),(2,4),(1,5),(1,6),(4,7)

3. Computer systems

   • Hardware and software
     • Hardware
       • Inputs
         • An input device is any piece of computer hardware used to provide data to a computer system.
         • Keyboard, mouse, scanner, webcam...
       • Outputs
         • Monitor, speaker, headphones, printer...
         • An output device is any piece of computer hardware used to communicate the results of data that has been processed.
   • Boolean logic
     • AND Gates
       • Is true when both of the inputs are true
     • NOT Gates
       • Is true when the input is not true
     • OR Gates
       • Is true when either of the inputs are ture
   • Software classification
   • Systems architecture