Computer Architecture

• Central Processing Unit is the primary component of a computer system that acts as its “control center”, this is where most of the calculations and controlling takes place. CPUs work extremely fast and hard, hence they generate a lot of heat
• Arithmetic Logic Unit

  Part of the CPU that does all the arithmetic (+/-) and logical (AND/OR) calculations. Sometimes an ALU is referred to as a ‘core’, and computers with dual core technology have two ALUs to process two calculations simultaneously.
• CU: Control Unit

  It handles the loading of new commands into the CPU and the decoding of these commands. Also, it directs the data flow and the operation of the ALU
• Registers are temporary storage areas inside the CPU used to store small instructions or small pieces of data as it is being processed. Registers are very small and have very fast memory situated very close to the ALU. 
• • MAR: Memory address register 

  MAR is connected to the address bus. MAR contains a memory address, it saves the position on the RAM that the CPU wants next either for reading or writing 
• • MDR: Memory data register. 

  MDR holds data that will be written to the RAM or that was read from RAM.
• • Program counter

  Stores the memory address that holds the next instruction to be read. The incrementor changes the program counter from one instruction to the next and the increment is controlled by the clock through the control unit. 
• Busses are the connecting wires that connect the CPU to other devices, carrying instructions to/from components. 

  The three most important busses are: - Data bus (links RAM to CPU via MDR) - Control bus (links RAM to CPU via CU) - Memory bus (links RAM to CPU via MAR)
• The machine cycle consists of four main steps: Fetch, Decode, Execute, and Store, used to describe the flow of data through the CPU. 

  Shows how the data is fetched from memory, decoded (CU), and then executed (ALU). 
• Accumulator

  Type of register used to store temporary values, usually for values that will go or come from the ALU.
• Fetch Phase:

  • During the fetch phase, the CPU retrieves the next instruction from memory. The PC is typically incremented for the next instruction in memory, preparing for the next fetch operation.
• Decode Phase:

  • In the decode phase, the CPU interprets the instruction, and determines the operation to be performed (arithmetic operation, data movement, branching, etc.).
• Execute Phase:

  • The execute phase is where the actual action takes place. Depending on the instruction, the CPU may perform arithmetic or logic operations, access memory to read or write data, or interact with input/output devices.
• Store Phase (Optional):

  • In some cases, particularly for instructions that produce a result, the store phase is used to store the result back to update CPU registers.
  • For example, in an arithmetic operation, the result might be stored in a designated register. 
  • Not all instructions require a store phase.