1.1

• Secondary storage is the memory in which the computer can store the data or instructions which are NOT currently in use.
• The main types of secondary storage are:

  • Hard Disk Drive (HDD).
  • Solid State Drive (SSD).
  • Compact Disc (CD).
  • Flash (USB Drive).
• Primary storage is the memory in which the computer can store the data or instructions that are currently in use.
• The two main types of primary storage are:

  • Random Access Memory (RAM).
  • Read-Only Memory (ROM).
• A processor is a special component that processes data and instructions to control other components within the computer.
• The two main types of processor are:

  • Central Processing Unit (CPU).
  • Graphics Processing Unit (GPU).
• I/O devices allow users to input data into the computer, or receive a data output from the computer.
• General purpose systems are capable of performing many different tasks.
• An embedded system is a computer system which is built into another device to support its operation.
• The ALU performs all of the arithmetic and logical operations of the CPU, including:

  • Addition and subtraction, multiplication and division.
  • Comparisons such as whether numbers are equal or if one is greater than another.
  • Boolean operations (e.g. AND, OR, NOT).
• The Control Unit transmits control signals to other components of the CPU.
• The Control Unit follows the fetch-decode-execute cycle to execute program instructions.
• There are two main components of the Control Unit:

  • The clock, which coordinates the CPU's activity.
  • The decoder, which decodes program instructions.
• Registers are tiny amounts of super-quick memory within the CPU.

  • They are used to hold information needed for the CPU to work.
  • Each register holds a specific piece of information.
• The accumulator holds the result of calculations and operations performed by the arithmetic logic unit (ALU).
• The Program Counter (PC) holds the memory location address of the next instruction to be performed by the CPU.
• The Memory Address Register (MAR) holds the address of the location in memory where data is to be retrieved or stored.
• The Memory Data Register (MDR) holds the data that has been retrieved from memory, or that is about to be stored in memory.
• Registers with a predetermined purpose in the central processing unit are known as special purpose registers.
• Arithmetic and Logic unit


  Performs CPU operations such as comparisons and Boolean operations.
• Control Unit


  Made up of two key parts; the clock and the decoder
• Registers


  Tiny amounts of super-quick memory within the CPU. Used to hold specific pieces of information needed for the CPU to work.
• Decode


  The Control Unit decodes the instruction and sends control signals to the component within or outside the CPU that needs to act.
• Fetch


  • The address of the instruction that needs to be processed next is copied from the Program Counter (PC) to the Memory Address Register (MAR).
  • The PC is incremented to point to the next instruction that will be needed when the cycle starts again.
  • The instruction stored at the location held by the MAR is copied to the MDR.
• Execute

  • The operation indicated by the instruction is performed by the appropriate component. For example:
  • The Arithmetic Logic Unit (ALU) performs the operation given by the Control Unit.
  • The value stored by the Program Counter or Memory Address Register might be changed.
• Cache memory is a small amount of very fast memory inside the CPU.
• In comparison to the cache, accessing the Random Access Memory (RAM) is a very slow operation.
• By storing frequently accessed data and instructions in cache memory we can avoid the process of accessing the RAM.
• The CPU's clock sends a pulse at fixed intervals to trigger the next stage of the fetch, decode, execute (FDE) cycle.
• The higher the clock speed, the more pulses are sent per second, so more instructions can be executed in the same amount of time.
• • Each core of a CPU is capable of processing instructions independently.
  • Each core has its own Control Unit (CU), and Arithmetic and Logic Unit (ALU), but the cores share access to cache and main memory.
  • Multiple cores allows a CPU to process multiple instructions at the same time.