A microprocessor is an electronic device capable of manipulating data to produce desired results. The functions of a digital computer are performed using the microprocessor’s arithmetic, logic and control circuitry. It essentially consists of several hundred thousands, or perhaps even billions of tiny transistors on a single integrated circuit.
Every microprocessor depends on an ‘instruction set’, which is designed to program it to perform specialized functions.

Main parts of microprocessors

Microprocessors consist of several different parts:

1. The arithmetic and logic unit (ALU), which performs calculations and logical outputs.
2. Registers, in which temporary data is stored.
3. The control unit which decodes the programs fed into the processor.
4. The address, data and control buses, which exchange information to and from the various parts of the microprocessor system.

More advanced microprocessors series consist of an additional component called the cache memory that speeds up memory access and processing.
A crystal oscillator in a computer system provides a clock signal to govern the functioning of the microprocessor, helping it carry out billions of instructions per second.

Types and uses
Microprocessors are popularly classed according to the number of bits that they can manipulate. For instance, a microprocessor with an arithmetic and logic unit which can manipulate data 4-bits wide is referred to as a 4-bit microprocessor. This form of classification does not take into account the number of address bus lines (the channel which sends out addresses of memory locations or ports) or data bus lines (the channel which sends data to/from memory or ports).
Another way of classing microprocessors is as embedded controllers, also referred to as dedicated controllers or microcontrollers. These pre-programmed devices consist of not just a basic microprocessor, but also random-access memory (RAM), read-only memory (ROM) and input/output capabilities all integrated onto one and the same chip. These are used to control ‘smart machines’ such as programmable washing machines and microwave ovens.
One or more microprocessors typically make up a central processing unit (CPU) in a particular application using a computer system. In this way, scientific and business tasks can be effectively handled. Microprocessors are needed for a wide variety of applications from simple calculators to the largest mainframe computers and hand-helds.

History and development
The earliest microprocessors appeared in the 1970s with the development of Large Scale Integration (LSI) in integrated circuit technology, which made it possible to accommodate several thousand transistors, resistors and diodes onto a single silicon chip. With the advent of Very Large Scale Integration (VLSI) in the 1980s it became possible to fit several hundred thousand components onto chips not larger than 5mm square in size.
Some of the earliest microprocessors were Intel’s 4004 and Texas Instruments’ TMS 1000, both 4-bit microprocessors. Later, the 8-bit Intel 8008 was made in 1972. The more advanced 8080 had a larger instruction set than its predecessors. It used NMOS transistors, and was referred to as a second generation microprocessor. Around the same time, Motorola came up with its MC6800, also an 8-bit microprocessor.

Embedded controllers
An evolution in three different directions has been seen as far as microprocessors are concerned. The first direction is that of the embedded controllers. Examples are the 8051 series of Intel and Atmel’s 89C51/2.

Bit-slice processors
A second direction has been that of the bit-slice processors. Bit-slice processors have components that can work in parallel to manipulate 8-bit, 16-bit or 32-bit words. AMD’s 2900 family of processors is an example of this category.

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