Data integrity and sanity check

Hi,

someone asks me about an utility to check any PostgreSQL database
data to be sure that:
1) there is not any page corrupted
(by a memory fault or a damaged disk)
2) re-check any constraint inserted into the database

I really don't know if PostgreSQL itself has any crc check on
its pages. Please, there is anyone able to confirm such function?

I've understood that PostgreSQL trust the operating system for
doing its work, but I don't know if there is any operating system
able to give warranty the memory sanity before allocation, during
the memory use.

According to me, if the database is well-designed it's not
possible to find constraint violation on data already inserted
and accepted from the SQL engine.
Am I in fault for this sentence?

Thank you in advance for any reply.

Best regards, \fer