Disk Access Question

I have a question on disk access.

How often is PostgreSQL accessing/touching the files that are on the hard drive?

What I'm trying to ask is, is PostgreSQL constantly updating access timestamps or something like that on the database files even if they are not being queried?  This questions comes from an Oracle background where Oracle was updating the individual files every 3 seconds if I am remembering correctly.

I am trying to figure out besides the queries, what sort of accessing is PostgreSQL doing to my drives so we can try and resolve some i/o issues.

Thanks,

Chris