What are the differences between ROM, PLA, and PAL?

These are programmable logic devices: ROM (Read-Only Memory) has fixed AND array (full decoder) and programmable OR array, implementing any function but inefficient for sparse truth tables. PLA (Programmable Logic Array) has both programmable AND and OR arrays, most flexible but complex and slow. PAL (Programmable Array Logic) has programmable AND array and fixed OR array, simpler than PLA with faster operation. Modern equivalents are CPLDs and FPGAs. Selection depends on function complexity, speed requirements, and available device resources.