Computer Science

• Control Unit


  Oversees the fetch decode execute cycle
• Arithmetic Logic Unit (ALU)


  The part of the central processing unit that performs arithmetic computations and logical operations.
• Cache


  High speed small storage memory used for storing frequently use instructions
• Registers


  Specific memory that stores data, the CPU is currently processing
• Program Counter (PC)


  The register that contains the address of the next instruction to be executed
• Memory Address Register (MAR)


  Stores the memory address of instructions being searched for
• Memory Data Register (MDR)


  Holds the data/instructions that are to be read/written
• Accumulator


  Where intermediate arithmetic and logic results are stored.
• Fetch


  Instruction is fetched from the memory address which the program counter is currently holding, once this is passed over program counter increased by 1
• Decode


  The memory address provides the location of the memory data to be used, which is decoded by the control unit
• Execute


  The instruction is carried out, and the results are stored in the accumulator with any memory data register being updated as needed
• Core


  Are processing unit found within the CPU
• Clock speed


  Increase performance by performing more instructions per second measured in hertz
• Cache size


  High speed, small storage memory that holds frequently used instructions which makes routine processes faster. However, too much is bad as you only want to instructions, else it takes too long to search.
• Number of cores


  The more cause the more instructions carried out, however, 2 to 4 cores doesn't double the speed
• RAM (Random Access Memory)


  Volatile and often use to hold data/instructions that are currently in use.
• ROM (Read Only Memory)


  Non-volatile and tends to hold operating system information as well as information such as boot up instructions
• Virtual Memory


  Where RAM becomes full, and space from secondary storage is used to temporarily act as RAM. Once the need for this and secondary storage passes data back to RAM.
• Primary Storage


  Needed to store files the CPU is currently accessing.
• Secondary Storage


  Long term permanent storage of files, without it, we'd rely on volatile primary memory which is smaller than secondary
• Optical


  Consists of CD, DVD's and Blu-ray. Read by laser in 1 or 0 binary values.
• Magnetic


  Magnetised disk which uses a reader head which moves as the disk spins
• Solid State


  No moving parts, very fast, data kept trapped in electronic gates
• Optical


  Low capacity Low speed Medium portability Low durability Medium reliability Low cost
• Magnetic

  High capacity Medium speed Low portability Low Durability Medium reliability Medium cost
• Solid State


  Medium to High capacity High speed High portability High Durability High reliability High cost
• ASCII


  A 7-bit character set consisting of 128 characters
• Extended ASCII


  an 8-bit character set consisting of 256 characters
• Unicode


  A character code that enables most of the languages of the world to be symbolized with a special character identification.
• 8 bits


  1 byte
• 4 bits


  1 nibble
• 2 nibbles


  1 byte
• 1000 bytes


  1 kilobyte
• 1000 kilobytes


  1 megabyte
• 1000 megabytes


  1 gigabyte
• 1000 gigabytes


  1 terabyte
• 1000 terabytes


  1 petabyte
• Resolution


  Width x height x colour depth
• More bits


  Higher quality and bigger file
• 4 mins, 40kbps, 20 bit rate

  (240)x40x20=192000/8 bits =24000KB/1000=24MB