Components of a computer system

• Hardware is the physical components, such as the CPU, Motherboard, monitor and printer.
• Software is the programs or applications that run on a computer system, e.g Operation system, video game
• Embedded systems are computers that are built into other devices. Examples include dishwashers and washing machines
• The CPU is the central processing unit of a computer, which is responsible for processing instructions and data that make the system work.
• The Control Unit

  • Manages the fetch-decode-execute cycle of the program instructions
  • Controls the flow of data inside and outside the CPU
• The ALU is the arithmetic logic unit which performs calculations and performs logical operations such as AND, OR, NOT.
• The Cache

  • Very fast memory in the CPU, but slower than registers
  • Stores regularly used data so that the CPU can access it quickly the next time it is needed.
• The program counter is a register in the CPU that holds the memory address of the instruction of each cycle
• The accumulator stores intermediate results of the calculations in the ALU.
• The MAR(memory address register) holds any memory address about to be used by the CPU. The register may point to a data or an instruction
• The MDR( Memory data register) holds the actual data or instruction
• Fetch, decode, execute cycle:

  Fetch stage:

  • CPU copies memory address from the program counter to the MAR
  • Copies instructions stored in the MAR address to the MDR
  • Increments the program counter to point to the address of the next instruction, ready for the next cycle

  Decode stage:

  • Instructions in the MDR is decoees by the Control unit. The control unit may then prepare for the next step

  Execute stage:

  - The instruction is performed. This could be: load data from the memory, write data to memory, etc
• Volatile memory is temporary memory. It requires power to retain its data
• Non-volatile memory is permanent memory- it keeps its contents even when it has no power
• RAM( Random access memory) is used as the main memory in a computer. It is an example of volatile memory
• Virtual memory is an area of secondary storage that the computer uses to store the contents of RAM temporarily when there isn't enough space in RAM to store necessary software/data. The computer will copy the items not currently in use from RAM to virtual memory, freeing up space in RAM
• ROM ( Read only memory) is memory that contains all the instructions a computer needs to properly boot up. It is an example of non-volatile memory and it can be read, but not written