More on FPGAs...

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What is an FPGA?

    Before the advent of programmable logic, custom logic circuits were built at the board level using standard components, or at the gate level in expensive application-specific (custom) integrated circuits.  

The FPGA is an integrated circuit that contains many (64 to over 10,000) identical logic cells that can be viewed as standard components.  Each logic cell can independently take on any one of  a limited set of personalities.  The individual cells are interconnected by a matrix of wires and programmable switches.  

Basics on Programmable devices...

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1. When did PLDs come into picture and what is the reason behind that?

         In early 1960s there was discrete logic. Systems were built from lots of individual chips with a spaghetti-like maze of wiring between them. It was difficult to modify such a system after you built it. After a week or two it was difficult to remember what each of the chips was for!

Manufacturing such a system took a lot of time because each design change required that the wiring be redone which usually meant building a new printed circuit board. The chipmakers solved this problem by placing an unconnected array of AND-OR gates in a single chip called a programmable logic device (PLD).