1.1.1 Structures and Functions of a Processor

  • Created by: CubbyHD
  • Created on: 19-04-18 13:05

Components Of a CPU

  • CPU - This stands for the central processing unit of the computer and carries out the fetch decode execute cycle, in order to decipher information and then omit it to other parts, where the execution needs to take place.
  • ALU - This stands for the arithmatic logic unit and this is responsible for all of the calculations and logical operations that a computer needs to do.
  • Registers - These act as a temporary storage location for a process. This is so the information can be accessed quickly.
  • CIR - This is the current instruction register and this contains the operator and the operand of the instruction that is currently being completed.
  • MDR - This is the Memory Data Register and this is important, because it stores the data from the instruction that is on its way to be completed, or it will hold the data from and instruction that has already been completed, and is on it's way to another location in the CPU.
  • PC - The program counter is responsible for keeping track of what instrucion the computer is on.
  • ACC - The accumulator is a short term storage for all logical and mathematical solutions. 
  • MAR - This is needed so that the CPU can connect with the address bus.
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  • Data Bus - This typically consists of 8,16,32 or 64 separate lines providing a bi-directional path for moving data and instructions between system components.
  • Address Bus - This carries the address of the memory location being read from or written to.
  • Control Bus - a bi-directional bus meaning that signals can be carried in both directions. Control lines must therefore be provided to ensure that access to and use of data and address buses by the different components of the system does not lead to conflict. The purpose of the control bus is to transmit command, timing and specific status information between system components. 
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Cache Memory


Cache memory is memory that is a sort of RAM that can be accessed faster than the regular RAM. They are generically smaller than normal memory, however they are faster to access so they can be useful to store current instructions etc.

  • L1 + L2 - Level 1 and 2 are a way of saving time so that if the processor can find the data from level 1 or 2 then it can access it from there.
  • L3 - L3’s purpose is the significantly increase the speed of level 1 and 2.
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Computing Architecture

John von Neumann

Who was he? - He developed a theory that computers could have a fixed structure but could complete any instruction without any modification to the hardware.


Harvard architecture was an adaptation of the Von Neumann Architecure. The difference between the Harvard architecture and the Von Neuman Architecture is that the Harvard architecture has 2 buses, whereas the Von Neumann Only has one.

Overall, the Harvard architecture is more popular, as it gives the user the ability to access data and instructions at the same time, meaning that the overall time that it takes to complete tasks is reduced.

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