The generated numbers should not have repeating patterns which means the PRNG should have a very long cycle length. A PRNG is normally just an algorithm where the same initial starting values will yield the same sequence of outputs.
Some applications have criteria which affect the type of PRNG which is needed.
Many other operating systems also have random number device drivers and other related mechanisms, but largely make no use of them. OpenBSD deviates by actually using these mechanisms in numerous ways.