Logic circuits are used to build computer hardware, as well as many other types of products. All such products are broadly classified as Digital Hardware. It is derived from the way in which information is represented in computers, as electronic signala that correspond to digits of information.

• The technology used to build digital hardware has evolved dramtically over the past four deacdes. Until the 1960s logic circuits were constructed with bulky components, such as transistors and resistors that came as individual parts.
• The advent of ICs made it possible to place number of transistors, and thus an entire circuit, on a single chip.
• In the beginning hese circuits had only a few transistors, but as technology improved they become larger. ICs are manufactured on a silicon wafer.
• The wafer is cut to produce the individual chips, which is then placed in a special type of chip package. By 1970 it was possible to implement all circuitry needed to realize a microprocessor on a single chip.
• Although early microprocessor had modest computing capability by today's standards, they opened the door for the information processing revolution by providing the means for implentation of affordable personal computers.
• About 30 years ago Gordon Moore, chairman of Intel Corporation, observed that IC technology was progressing at an astounding rate, doubling the number of transistors that could be placed on a single chip every 1.5 to 2 years.This phenomenon, informally known as Moore's law, continues to present day.
• Thus in early 1990s microprocessors could be manufactured with a few million transistors, and by the late 1990s it became possible to fabricate chips that contain more than 10 million transistors. Presently chips can have a few hundreds of millions of transistors.
• Moore's law is expected to continue to hold true for at least the next decade. A consortium of IC manufacturers calle the Semiconductor Industry Association (SIA) produces an estimate f how the technology is expected to evolve.
• The size of a transistor is measured by a parameter called its gate length.
• In 2004 the minimum possible gate length that can be reliably manufactured is 90nm. The first row of the table indicates that the minimum gate length is expected to reduce steadily to about 35nm by the year 2012. The size of a transistor determines how many transistors can be placed in a given amoun of chip area, with the current maximum being about 30 million transistor per cm².
• This number is expected to grow to 100 million transistors bythe year 2012. The largest chip size is expected to be about 1300 mm² at that time; thus chips with up to 1.3 billion transistors will be possible!
• There is no doubt that this technology will have a huge impact on all aspects of people's lives.
• The designer of digital H/W may be faced with designing logic circuits that can be implemented on a sinle chip or, more likely, designing circuits that involve a number of chips placed ona printed circuit board (PCB).
• Frequently, some of the logic circuits can be realized in existing chips that are readily available. This situation simplifies the design task and shortens the time needed to develop the final product.
• There exists a large variety of chips that implement various functions that are useful in the design of digital harware. The chips range from very simple ones with low functinality to extremely complex chips.
• For example, a digital hardware product may requires a microprocessor to perform some arithmetic operations, memory chips to provide storage capability, and interface chips that allow easy connection to input and output devices. Such chips are available from various vendors.
• For most digital hardware, it is also necessary to built  logic circuits from scratch. For implementing these circuits, three main types of chips may be used: standard chips, programmable logic devices, and custom chips.