How Central Processing Units (CPUs) work?

The circuits that once required a roomful of vacuum tubes connected by miles of wire now resides on several small silicon chips, Inside modern computer’s microprocessor, RAM modules, ROM, clock, and other supporting circuit are interconnected on a single circuit board within the motherboard.

How does the processor stage-manage all of the actions involved in running a program? All processing, regardless of the operation, is broken into two phases: the instruction phase and the execution phase.

During the instruction phase, the processor’s control/communication operation identifies the next program instruction and its address in memory. The instruction is then loaded (fetched) into the processor and translated in an action the processor can perform.

Let’s analyze a scenario where you have to sell tickets for a concert;

  • The first instruction, locating the number of tickets, is recalled.
  • The execution phase starts at this point, with the processor transferring related data from memory or performing the appropriate arithmetic or logic operation on the data. With the completion of this execution phase, the next instruction phase begins.
  • The instruction/execution cycle is repeated for the single-ticket cost.
  • Once the cost and number of tickets are in the processor, the next instruction/execution cycle results in multiplying these values.
  • Then the result is returned to the designated memory address and completes the execution.

The processor uses the internal clock to regulate the transfer of data or instructions so the phases do not overlap. The repetition of the instruction/execution cycle continues until all program instructions have been processed. The speed of processing depends on the clock speed of the processing hardware.

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