IGCSE computer science

Denary

Base ten number system made up of ten digits (0-9) and is the number system that humans understand.

Binary

Base two number system made up of two digits (0 and 1) and is what computers use.

10011 in denary

19

25 in binary

11001

Hexadecimal

Base sixteen number system that is made up of 16 digits (0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F)

Benefits of hexadecimal:

• It is easier for humans to read

• It is a shorter way of representing binary values on screen

A6 in binary

1010 0110

1001 1110 in hexadecimal

9E

Bit hierarchy:

• Bit (1 or 0)

• Byte (8 bits)

• Kibibyte

• Mebibyte

• Gibibyte

• Tebibyte

• Pebibyte

• Exibyte

Analogue data

The type of data humans process.

Mono

1 channel

Stereo

2 channels

Bit rate formula:

Bit rate = frequency * bit depth * channels

Frequency formula:

Frequency = number of samples per second.

Sound file size calculation:

file size = bit rate * length of audio

Color depth:

The number of bits used to represent the color in each pixel.

File size of an image formula.

file size - number of pixels (w * h) * bit/color depth

Compress BBBBWWWBBWWW

B4 W3 B2 W3

How does asymmetric encryption work?

• An algorithm is used to generate a matching set if keys (public and private)

• The public key is accessible to whoever wants to send a message to the person

• The public key is used to encrypt the message

• The encrypted message is sent to the person

• Only the person with the private key and decipher the encrypted message

• The public and private keys are linked but cannot be derived from each other.

Compiler:

Translates high-level language programs into machine code.

Interpreter:

Translates high-level languages and executes the code line by line

Assembler:

Translates assembly language into machine code.

IDE functions:

• editor for writing code

• Error diagnostics for debugging

• Auto-completion