Also known as an instruction address register, PC, or instruction pointer, a program counter is a type of register found in the central processing unit (CPU) of a computer system. The purpose of the counter is to provide temporary housing for the next instruction to be executed in a sequence of instructions. As an instruction is retrieved and implemented, the program counter queues the next instruction in the string, effectively minimizing delays in executing the steps necessary to complete a task. Always pointing to the next instruction, the process keeps moving forward efficiently.
A central processing unit. The program counter is one of several different registers built into the CPU.
Although variations exist, the operation of a program counter within the central processing unit is relatively simple. When a new task is requested, the instructions needed to manage that task are retrieved from memory. This is typically accomplished by the CPU creating an address that is sent to memory, which responds by sending the instructions back to the unit as data over a data bus.
The program counter, as one of several different registers built into the CPU, performs the task of receiving each of the instructions in the task sequence. Keeping the logical sequence simplifies the forward progression of each step, completing the task. This logical progression is maintained by pointing to the data that should be used next, even when the previous data is in use, and then quickly pointing to the next data in the sequence as each instruction is executed in turn.
Depending on the program counter setting, the register can serve as a pointer to more than one instruction involved in a given currently executing process. With some register designs, the program counter not only points to the next process in the sequence, but also to the newly released instruction that is now in the process of being implemented. This specific design was thought to help maintain the balance of features, as well as help protect the forward movement of instructions with a higher level of efficiency.
The function of a program counter is essential for the successful execution of the instructions involved in any task. By pointing the way toward each instruction in the sequence, the counter helps provide a logical execution of those steps that lead to task completion quickly and efficiently. Without the use of this type of record, the potential for sequence interruption would increase and the chances of completing the task would be relatively small. By adding organization to the incremental step-by-step completion of all instructions, the program counter serves as a conduit that minimizes anomalies and keeps the process running smoothly.