Identifying 32 vs 64 bit OS?

[Jeremy DeHaan via Digitalmars-d-learn]

I am looking at these versions as described here: 
http://dlang.org/version.html

There are X86 and X86_64 version identifiers, but these 
specifically mention that they are versions for the processor 
type. Can they also be used to determine if the OS is running in 
32 vs 64 bits?