Microprocessors, also called processors or CPUs (for "Central Processing Unit"), are often referred to as the "brains" of computers because they execute programs. There are many different types of microprocessors, both in terms of capability and brand.
Microprocessor speeds are typically measured in megahertz (MHz), which measures the amount of processing cycles that can be performed per second in millions. Today's microprocessors have speeds upwards of 1500 MHz (or 1.5 GHz).
Multi-core processors utilize two or more microprocessing "cores" to allow for a much speedier system performance.
Intel is the leading microprocessor manufacturer. Its microprocessors include the Pentium, Celeron and Core lines.
AMD is Intel's main microprocessor rival. Its microprocessors include the Athlon, Turion and Phenom lines.
In 2006, Apple announced that they were discontinuing the use of PowerPC microprocessors, which had been in use since 1994, in favor of Intel microprocessors.