Processor Speeds Explained

Image by, courtesy of Henrique Pinto

Computer microprocessors function as the "brains" of a computer. These special electronic circuits are capable of processing millions of instructions per second.

However, it can be confusing sometimes to hear the different descriptions of microprocessors bandied about, such as "dual-core," "x64" and "bus speed," and thus determine which processor is "fastest." But once you understand what each description signifies, you can more easily choose the right microprocessor for your computer system.

Bus Speed vs. Processor Speed

Each computer motherboard comes with an electronic component called a crystal oscillator. This component serves as a timing mechanism, or system clock, for the computer system.

When the 80486 microprocessor was introduced by Intel in 1992, the microprocessor speed was equal to the system clock speed on the motherboard. In other words, a computer with a 25MHz 80486DX microprocessor had a crystal oscillator that also ran at 25MHz.

By 1994, microprocessors were designed to multiply the clock speed internally. For example, a 66MHz 80486DX2 microprocessor was still driven by a crystal oscillator running at 33MHz, but the microprocessor would internally double the clock signal, thus producing a microprocessor that could perform two operations in one clock cycle.

Because the speed of the microprocessor was now faster than the system clock speed, two different indicators are used to quantify speed as it relates to a microprocessor: System clock (or "bus") speed, and microprocessor speed (a larger number, which is a multiple of bus speed).

Single-Core vs. Multi-Core Processors

Central processing units, until 2006, had a single microprocessor which handled all of the processing duties and workload of the computer system. Even though a microprocessor may have been able to handle any one task easily, when multiple tasks were performed on the computer system (such as having multiple applications open at once), this would create a bottleneck that would slow the computer down.

In 2006, both AMD and Intel released a new type of central processing unit--the multi-core processor. This type of CPU uses two or more discrete microprocessors in one chip. The multiprocessor layout of this CPU allows for shared workload between the two microprocessors, thus improving overall performance.

Each processor in a multi-core CPU operates at the noted processor speed and bus speed. For example, a dual-core CPU with a listed speed of 2 GHz has two microprocessors each running at 2 GHz.

x86 Processors vs. x64 Processors

Microprocessors that are advertised as x86 processors are also known as "32-bit" processors. These microprocessors are capable of interpreting instructions that are 32 bits, or binary digits, wide.

Microprocessors carrying the x64 designation are also known as "64-bit" processors. These microprocessors are capable of interpreting instructions that are 64 bits wide, as well as 32-bit instructions.

A 32-bit processor is not as well suited to handle multiple open applications as a 64-bit processor. Therefore, even if the processor speeds are the same for both processors, a computer with a 64-bit processor will run faster than a computer with a 32-bit processor when multiple software applications are running at once.

Overclocking and Underclocking

As noted in "Bus Speed vs. Processor Speedm," the processor speed is a multiple of the system bus speed. With many computer motherboards, processor speed can be adjusted by using software to adjust the multiplication factor. Usually, the listed processor speed is the maximum rated frequency for which the processor will run reliably.

Overclocking a microprocessor involves adjusting the multiplier to make the microprocessor run faster than rated speed. However, overclocking can cause the microprocessor to overheat, and this can cause it to prematurely fail.

Underclocking involves reducing the multiplier to a value below the maximum rated frequency. Usually, there is no inherent danger to underclocking.

Which Processor Is Fastest, and Which Should I Buy?

For equal bus speeds, a multi-core, overclocked, 64-bit processor will run the fastest. However, depending upon how you intend to use your computer, you may not need to use the fastest microprocessor available. For users running one application at a time, a 32-bit, single-core processor may fit the bill.