CPU Definition

A central processing unit (CPU) is a type of processor that serves as the main logic and control unit of a computer.

A processor, also referred to as a microprocessor in the case of a highly integrated semiconductor device, is a device or system that performs logic operations. These terms and CPU are often used interchangeably.

A modern CPU consists of a single, tiny chip of specially produced silicon (usually a square centimeter or less) on the top surface of which are formed millions of transistors and other circuit elements using a sub-micron fabrication process. Each chip is housed in a high precision ceramic or plastic package and mounted on the motherboard (i.e., the main circuit board on a computer). This chip is also commonly referred to as a processor or as a microprocessor.

Although most personal computers have a single CPU, some high performance computers have multiple CPUs in order to further increase processing throughput (i.e., the amount of data that can be processed per unit of time).

Computers also contain other microprocessors, such as those in disk drives and other peripheral devices. These have much less power and are much lower in cost than CPUs, and they have the important role of relieving the CPU of the burden of having to deal with peripheral functions.

A CPU contains three main sections: (1) an arithmetic/logic unit, (2) a control unit and (3) registers. The arithmetic/logic unit contains circuitry that performs data manipulation. The control unit consists of circuitry for coordinating the machine's activities. The registers are high speed memory cells that are used for holding instructions for data that is currently being processed.

The CPU reads data from the main memory, which consists of RAM (random access memory) chips, by suppling the addresses of the appropriate memory cells along with a read signal. Likewise, it writes data to memory by providing the addresses of the destination cells together with a write signal.

The first electronic CPUs were formed from arrays of vacuum tubes. They were subsequently replaced by circuit boards containing large numbers of discrete (i.e., separate) transistors and other electronic components, and these, in turn, were later replaced by circuit boards containing large numbers of integrated circuits (ICs).

The world's first single-chip microprocessor was the Intel 4004, which was released by Intel Corporation in November, 1971. The four-bit chip contained 2,300 transistors and had a speed of 108KHz, and it was housed in a 16-pin ceramic DIP (dual in-line package), This was followed the next year by the world's first eight-bit microprocessor, the 8008, which contained 3,300 transistors and had a speed of 0.5MHz (and 0.8MHz for later versions).

Modern CPUs are vastly more complex and powerful. They typically contain tens of millions of transistors and are housed in high precision packages containing hundreds of pins. Most CPUs still have 32-bit operation, but the use of 64-bit chips is growing rapidly as their prices continue to come down. Speeds approaching 2GHz are now common, and some chips have speeds well in excess of this.

For example, Intel's new Core Duo microprocessor, which was released in January 2006, contains approximately 151 million transistors and is expected to eventually have speeds of as high as 2.5GHz. It is also the world's first low power dual core processor, featuring a power consumption of only 25W. A dual core processor is a CPU that combines two sets of processing circuitry into a single package in order to improve performance. The Core Duo is the first Intel processor to be used in Macintosh computers.

Created May 10, 2006.
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