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circuit card

See printed circuit board.

printed circuit board

A rigid, flat board that holds chips and other electronic components. The board is made of layers, typically two to 10, that interconnect components via copper pathways. The main printed circuit board (PCB) in a system is called a "system board" or "motherboard," while smaller ones that plug into the slots in the main board are called "boards" or "cards." See flexible circuit.

Etched Circuits
The "printed" circuit is an etched circuit. A copper foil is placed over a fiberglass or plastic base of each layer and covered with a photoresist. Light is beamed through a negative image of the circuit paths onto the photoresist, hardening the areas that will remain after etching. When passed through an acid bath, the unhardened areas are washed away. The finished layers are then glued together. A similar process creates the microminiaturized circuits on a chip (see chip).

Starting in the 1940s
Printed circuits were first used in the 1940s to connect discrete components together. By the 1960s, PCBs were widely used in all electronic systems, but still mostly connecting discrete components. Integrated circuits (chip) were emerging and added to the boards, and by the 1980s, PCBs were holding large quantities of chips. Today, printed circuit boards typically connect mostly chips with only a few discrete components, each chip containing from a few thousand up to hundreds of millions of transistors. See surface mount, via, discrete component, chip, card and motherboard.

Motherboard and Expansion Cards
This Baby AT board is an example of an early PC motherboard that used an ISA bus. It accepted both ISA and PCI cards containing peripheral controllers.

They Can Be Very Small
This WOW HD board from SRS, which has an audio jack for headphones on the end of the cable, creates a more dynamic audio experience for music listeners. The complex processing that takes place on this tiny board was unthinkable in the early days of computing. (Images courtesy of SRS Labs, Inc.,

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Before/After Your Search Term
cipher negotiationcircuit cellular
cipher strengthcircuit-level proxy
cipher suitecircuit switching
ciphertextcircuit trace
CIRcircular buffer
circuitcircular polarization
circuit analyzercircular reference
circuit bendingcircular wait
circuit boardcircut
circuit breakerCIS

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