computer science

1.     A computer system uses hardware and software to input, process and output data and instructions.

2.     The CPU fetches an instruction from memory. Then it decodes it to find out what processing to do. Finally, it executes the instruction

3.     Hardware consists of all the parts of a computer that you can physically touch, e.g. keyboard, mouse.

4.     Software is the name for the programs and applications that run on a computer, e.g. safari, Microsoft teams

5.     An input device sends data and control signals to a computer. Examples: mouse, keyboard, touch screen, microphone, scanner, webcam.

6.     An output device communicates the result of processing. Examples: monitor/screen, printer, speakers, headphones.

7.     Computers use memory to store programs and data temporarily (currently being used by the computer). Contents are lost when the computer is off. Example: RAM

8.     Storage devices store data and files permanently. Examples: Hard disk drive (HDD), USB stick, CD, DVD/Blu-ray.

9.     Computers use binary numbers because the CPU is made of tiny electronic switches that have only 2 states - they are either "off" or "on", "0" or "1".

10.   How to convert an 8-bit binary number into a denary/decimal number and vice versa

11.   How to add together two 8-bit binary numbers. Rules: 0+1 = 1, 1+1 = 0 (carry 1), 1+1+1 = 1 (carry 1)

12.   Units:

13.   Unit calculations:

There are 8 bits in a byte

There are 2 nibbles in a byte

There are 1024 bytes in a KB

There are 1024 KB in a MB

There are 1048576 KB in a GB (1024*1024)

14.   Calculating the exterior angles of regular polygons: Formula = 360/number of sides

15.   An algorithm is a set of step-by-step instructions to describe a task or process.

16.   Decomposition means breaking down complex problems into smaller, easier to solve parts

17.   A flowchart is a visual method for describing algorithms. Symbols are linked together with arrows

18.   Sequence: A set of instructions that must be followed one after another in a specific order

19.   Selection: The choice of which route to take through a computer program

Selection in a Python program uses an IF statement

20.   Iteration: Using repetition of a process to create a more efficient solution

Iteration in a Python program uses a FOR loop

21.   Pseudocode is a simple but structured way of writing algorithms

22.   Recognising errors in a Python program. Learning the syntax e.g. when quotation should be used, when to use a single or double = sign, where brackets should go etc.

23.   A variable is a location in RAM used to store values while the program is running.

You also need to be able to read algorithms and see how the variable values are changing

24.   Variables have a data type. Common data types are:

·       String (text, numbers, spaces, symbols)

·       Integer (whole number)

·       Real (a number that can be a decimal)

·       Boolean (can only be one of two values, True or False)

25.   The double asterisk means ‘to the power’ e.g. of 5 ** 2 (meaning 5 to the power of 2) = 25

DIV means integer division. It divides two values and rounds down the answer e.g. 5 // 2 = 2

MOD means modulo division. It gives the remainder of a division between two values e.g. 5 % 2 = 1

26.   Interpreting algorithms. Reading through a flowchart or pseudocode algorithm to determine the inputs, outputs and variables, in both Scratch and Python

24.   A pixel is a "picture element".  Typically a tiny square or dot that contains a single point of color of a larger image

25.   Metadata is “data about the data” that is required to encode or decode the bits e.g. resolution, author, date

26.   Resolution is the density/number of pixels in an image. Resolution is calculated by multiplying the width*height of pixels in an image

27.   Colour depth is the set number of colours available for each pixel.

E.g. 6 bits per pixel means 2⁶ = 64 possible colours

28.   How the file size of an image is calculated: resolution*colour depth = file size in bits

E.g. This image is 4x4 pixels wide/high, it has a colour depth of 1 (2¹ = 2 colours)

Therefore, 4*4*1 = 16 bits

29.   Increasing the resolution or the colour depth of an image improves the quality of an image but also increases the file size

Useful resources:

·       Student Portal > KS3 > Computer Science > Resources to help you revise.

·       BBC Bitesize KS3 Computer Science:

o   Hardware and software

o   Programming

o   Algorithms

o   Data representation