PLD’s (Programmable Logic Devices) are the circuits that contain an array of AND gates and another array of OR gates. There are three kinds of PLD’s depending upon the type of array, i.e.
Programmable Read-Only Memory
Programmable Array Logic
Programmable Logic Array
ROM is a memory device that stores the binary information permanently.
PROM:
It is known as programmable read-only memory
It includes both AND array & OR array
Out of these two arrays AND array is fixed and OR array is programmable.
PAL: Programmable AND array followed by fixed OR array
PLA: Programmable AND array followed by Programmable OR array.