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What Is a Program Counter?

A central processing unit. The program counter is one of several different registers built into the CPU.
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  • Written By: Malcolm Tatum
  • Edited By: Bronwyn Harris
  • Last Modified Date: 12 October 2014
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Also known as an instruction address register, PC, or instruction pointer, a program counter is a type of register that is found in the central processing unit (CPU) of a computer system. The purpose of the counter is to provide the temporary housing for the next instruction that is to be executed in a string of instructions. As one instruction is retrieved and implemented, the program counter queues up the next instruction in the string, effectively minimizing delays in the execution of steps necessary to complete a task. By always pointing at the next instruction, the process is kept moving forward efficiently.

While there are variations, the operation of a program counter within the central processing unit is relatively straightforward. When a new task is ordered, the instructions necessary to manage that task retrieved from the memory. This is normally accomplished by the CPU creating an address that is then sent to the memory, which responds by sending the instructions back to the unit as data via a data bus.

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The program counter, as one of several different registers built into the CPU, performs the task of receiving each of the instructions in task sequence. Maintaining the logical sequence simplifies the forward progression to each step, ultimately completing the task. This logical progression is maintained by pointing to the data that is to be used next even as the previous data is in use, then quickly pointing to the next data in the sequence as each instruction is executed in turn.

Depending on the configuration of the program counter, the register may actually serve as the pointer for more than one instruction involved with a given process currently under execution. With some register designs, the program counter not only points toward the process that is next in the sequence, but also toward the just released instruction that is now in the process of being implemented. This particular design is thought to aid in maintaining the balance of resources as well as helping to protect the forward movement of the instructions with a higher level of efficiency.

The function of a program counter is essential to the successful execution of the instructions involved in any task. By pointing the way toward each instruction in the sequence, the counter helps to provide a logical execution of those steps that ultimately lead to completing the task quickly and efficiently. Without the use of this type of register, the potential for the sequence to be disrupted would be enhanced, and the chances for completing the task would be relatively few. By adding organization to the incremental step by step completion of all instructions, the program counter serves as the conduit that minimizes anomalies and keeps the process moving forward properly.

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