Question about storage subsystem of PotgreSQL

Hi

I want to find some architectural information about the storage
subsystem of PostgreSQL especially the modulus which are responsible to
loading data from disk to the Shared Buffer.  I cannot find any
structured and useful information on web.

Would you please help me to find such information.

Should I read the source code?

Which part of code is responsible to reading data from the disk?

Regards

Javadi