What is the difference between a PAL and a PLA?

PLA is programmable logic array while PAL is Programmable Array Logic.

PLA is a kind of programmable logic device used to implement combinational logic circuit.
It has Programmable AND Gate linked with Programmable OR Gate.

PAL is an combinational PLD that was developed to overcome certain disadvantage of PLA.
PLA shows longer delay due to additional fusible links which results from using two programmable array and increase circuit complexity.
Thus, PAL is used which is less complex and fast to implement. PAL consists of programmable AND linked with fixed OR.
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