A computer's "brain" is its central processing unit (CPU). In ordinary operation, the CPU processes all operations for the computer, allowing programs to run and the operating system to function. CPUs vary in their speed and efficiency. The primary determinant for the performance of a computer's CPU is the clock speed of the CPU unit, which measures the number of basic arithmetic operations — addition, subtraction, multiplication, or division — it can perform each second. Frequency scaling is the most basic way to eke more performance from a processor; by increasing the clock frequency, which is the speed at which the CPU runs, the computer's performance will also increase.
Until recently, with the advent of multi-core processors, frequency scaling was the most elementary way to garner additional performance for new processor models. Older processors used to run at a below 1.0GHz in speed. Now, processors commonly run at speeds greater than 2.0GHz, with some topping the 3.0GHz mark. On paper, a 3.0GHz CPU "looks" faster than a 2.0GHz CPU, but in the real world, the overall performance of the computer is determined by an aggregate of all its parts. In other words, if both the 2.0GHz and 3.0GHz computers contain the same type of memory, the same motherboard, and so forth, the weakest link in the chain can "bottleneck" the computer, preventing it from optimizing all 3.0GHz.
Although it might seem as though frequency scaling has no ceiling, that is not the case. Increasing the clock speed of a CPU increases heat production in the unit; over time, this extra heat acts to degrade the circuitry, causing the processor to malfunction or fail. This places a very real ceiling on the maximum speed of commercial processors, limiting the speeds at which processors can be built.
Increasing CPU performance in the absence of frequency scaling requires more innovative solutions; CPU manufacturers can no longer simply "turn the volume up" to elicit more performance. To work around these limits, CPU manufacturers have designed multi-core CPU solutions. By placing more than one CPU core on a chip, the effective speed of the processor is doubled. However, unlike frequency scaling, whose performance boosts apply equally across the board, this places the onus on computer software designers. Unless software designers specifically tailor a program to use two or more CPU cores, the extra benefit is lost, making frequency scaling one of the purest ways of increasing performance on a CPU chip.