• Units of storage: bit, byte, Kilobyte, Megabyte, Gigabyte, Terabyte, Petabyte
• Translation of high-level program code to binary (machine code): interpreters and compilers
• Use of binary to represent and store:
  • Integers
  • Real numbers (mantissa & exponent)
  • Characters
  • Instructions (machine code)
  • Graphics (bit-mapped and vector)
• Basic computer architecture:
  • Processor( registers, ALU, control unit)
  • Memory
  • Buses (data and address)
  • Interfaces

Units of storage

Binary / Decimal

128 64 32 16 8 4 2 1 
 1  1  1  1  1 1 1 1 = 255 
 0  1  1  0  1 0 0 1 = 105

• 1 bit  = Binary Digit
• 8 bits = 1 Byte
• 1024 Bytes = 1 Kilobyte
• 1024 Kilobytes = 1 Megabyte
• 1024 Megabytes = 1 Gigabyte
• 1024 Gigabytes = 1 Terabyte
• 1024 Terabytes = 1 Petabyte

Translation of high-level program code to binary (machine code)

• Interpreters – translates program code line by line, spots errors more easily but takes longer.
• Compilers – translates program code and saves the machine code, less likely to spot errors but more efficient. Creates a run time version that can’t be edited.

Use of binary to represent and store

• Real numbers uses mantissa & exponent – 2.56 X 10⁵
  • Mantissa = 2.56 Exponent = 5
• Characters – ASCII allocates a different binary code to each letter (8 bits-256 characters), Unicode (16 bits – 65,535 characters)
  • A = 00100001
• Instructions, machine code – the only characters the processor can understand 10101011101
• Graphics bit-mapped and vector Bit-mapped, graphics are made up of pixels

Bit-mapped Graphics

Formula

Number of pixels = image width x resolution x image height x resolution

Example 1

This is enlarged but is 1 inch by 1 inch at 22 Dots Per Inch. In that case there are 22 x 1 x 22 x 1 = 484 pixels

Example 2

Bitmap with a resolution of 600×600 pixels in 8 bit colour.

Storage requirements

600 x 600 x 1 bytes = 360000 
It is 1 byte as it is 8 bits per pixel 
360000/1024 = 351.6 kilobytes

Example 3

Calculate the number of pixels in 4 inch by 5 inch photograph scanned which has a resolution of 600 dots per inch.

Pixels = 4 x 600 x 5 x 600 = 7,200,000 pixels
1pixel = 1 bit 
7,200,000 / 8 = 90000 bytes 
90000 bytes / 1024 = 878.9 Kb

Vector Graphics

It is possible to edit each object separately, for example, change the shape, colour, size and position.

Even if an object in a vector graphic is quite large, it doesn’t need a lot of computer memory. Therefore the file size of a vector graphic is often very small.

Vector graphics are scalable when you resize them, they do not lose quality.

Basic computer architecture

• Processor
  • Registers – temporary storage locations holding data being processed
  • Arithmetic and Logic Unit – deals with comparisons and arithmetic calculations
  • Control Unit – controls all other parts of the processor, ensures instructions are carried out in the correct order

• Memory
  • Random Access Memory (RAM) – temporary data storage only held as long as the computer is switched on.
  • Read only memory (ROM) – Permanent memory not lost when the computer is switched off. Data stored on a hard disk or a memory stick.

• Buses
  • data bus – carries data to and from the processor, memory and other devices. Bi-directional
  • address bus – carries address locations from processor to the memory.
  • control bus – made up of a number of separate wires.

• Interfaces
  • allows a processor to send and receive data to and from peripherals like printers, scanners, keyboards and projectors.