Source : Free On-Line Dictionary of Computing

printed circuit board
     
         (PCB) A thin board to which electronic components
        are fixed by solder.  Component leads and {integrated circuit}
        pins may pass through holes ("vias") in the board or they may
        be {surface mounted}, in which case no holes are required
        (though they may still be used to connect different layers).
     
        The simplest kind of PCB has components and wires on one side
        and interconnections (the printed circuit) on the other.  PCBs
        may have components mounted on both sides and may have many
        internal layers, allowing more connections to fit in the same
        board area.  Boards with internal conductor layers usually
        have "plated-through holes" to improve the electrical
        connection to the internal layers.
     
        The connections are metal strips (usually copper).  The
        pattern of connections is often produced using photo-resist
        and acid etching.  Boards, especially those for high frequency
        circuits such as modern {microprocessor}s, usually have one or
        more "{ground plane}s" and "power planes" which are large
        areas of copper for greater current carrying ability.
     
        A computer or other electronic system might be built from
        several PCBs, e.g. processor, memory, graphics controller, disk
        controller etc.  These boards might all plug into a
        {motherboard} or {backplane} or be connected by a {ribbon
        cable}.
     
        (1995-05-01)