Takes two to tango

Like any good building set, digital logic needs only a handful of parts to achieve many different ends. Two different types are in fact all it takes. All that needs to be added to the inverter of the previous page is an andgate and then the set is complete. An andgate has two inputs and produces a true output if both of its inputs are true and a false output if either of its inputs are false.

The andgate is the little structure on the left halfway up. Everything else is there to provide glider streams. The inputs come from the top and bottom, the output leaves to the right. When no gliders come in then no gliders go out. A single glider from either the top or bottom is blocked. Two gliders, however, conspire to produce an output glider.

The CPUs of real computers can be built out of collections of electronic andgates and inverters. The collection is usually pretty big.

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Brian Silverman
Note: This page has Java content.