How The Central Processing Unit (cpu) Works

A CPU has two primary tasks: processing data and executing instructions. The processor contains a quartz clock that sends out tiny pulses of electricity at regular intervals. Each time the clock ticks, the CPU can process one piece of data or execute one instruction.

While it might appear that the processor can do many tasks at once, it can really process only one instruction at a time. However, it processes the instructions so quickly that it appears to be multitasking. A CPU with a clock speed of 3 GHz, for example, can process three thousand million instructions per second.

When you insert a DVD into an optical drive, the program you’re running might pause for a moment. While the CPU is busy processing instructions for the program, devices such as a DVD drive, printer or camera might need CPU resources to complete an operation. To let the processor know it needs attention, a device signals an interrupt. When the processor is interrupted, it stores its current state in memory, executes instructions for the device, and then restores its prior state and continues running the program where it left off.

The difference between a slow computer and a fast computer is the power and speed of the processor, which are driven by the number of transistors on the processor’s chip and its clock cycle. Advances in technology have enabled processor manufacturers to place an increasing number of transistors on a single processor chip to create powerful processors that fit in small devices such as mobile phones and tablets. A typical smartphone has about 193,000 percent more transistors on its processor chip than a personal computer from the early 1990s, and its clock runs about 16,600 percent faster.

A computer with two processors runs almost twice as fast as a computer with a single processor. Placing multiple processors on a single chip is another common method of manufacturing faster computers. Displaying computer graphics requires a substantial number of processor cycles, which can slow down the other tasks that a computer performs. To relieve the CPU, manufacturers developed the graphics processing unit, or GPU. A CPU often has a built-in GPU on the same chip. The two processors work in tandem to provide the resources demanded by the device, with the CPU offloading much of the graphics work to the GPU.