Most of us who own computers realize that microprocessors have increased the speed and performance of our machines in the last few decades, which is why many of us say that once we buy a machine it almost seems immediately obsolete. In other words, a computer we had a decade ago seems to most of us to be very, very slow compared to the processing speed of today’s computers; it’s all thanks to the development of better microprocessors.

Mainframe computers like these can fill a room in a company’s office, but smaller businesses that did not have the money or space for mainframes once used smaller mainframe units called minicomputers. By the late 1980s, microcomputers had become powerful enough to replace minicomputers.

The clock speed, also called the clock rate, is the speed at which the microprocessor of a computer executes instructions. In every computer, an internal clock is responsible for maintaining the rate of the instructions, even synchronizing the other computer components, such as the internal digital clock and date. Clock speed is measured in kilohertz (KHz, sometimes seen as KiloHertz), megahertz (MHz, sometimes seen as MegaHertz), or gigahertz (GHz, sometimes seen as GigaHertz). To understand this measurement, for example, 200 MHz is ten times the speed of 20 MHz; 1 GHz is simply equally to 1,000 MHz, and so on.

Overall, the faster the clock speed, the more instructions can be carried out by the computer’s CPU, or the central processing unit. For example, in 1974, the Intel 8080 processor had a clock speed of 2 megahertz (MHz). The original IBM PC (International Business Machines Personal Computer) around 1981 had a clock rate of 4.77 MHz (that translates to 4,772,727 cycles per second). In 2004, the Pentium 4 (“Prescott”) had a clock speed of 3.6 GHz (some say 3.4); and as of this writing, the highest clock speed microprocessor ever sold commercially is IBM’s zEnterprise 196 mainframe, which, as of 2010, ran cores (“many-core” chips use an array of many processors) continuously at 5.2 GHz.