Pointers in B Tree

Pointers in B Tree

I read about B trees and understand their input, delete methods. I read
with an introduction like this:
When we build structures on disk, we must deal with certain realities of
access and transfer time:
Random access to disk typically requires on the order of 10-20 ms access
time to position the head and wait for data to come up under it.
Once the head position is right, data can be transferred at rates in
excess of 1 million bytes/sec.
Observe, then, how total transfer times behave for different size blocks
(assuming a fairly fast 10 ms access time, and 1 megabyte/sec transfer
rate)
So, B Tree Data Structure is made for serving from disk ( which is what
makes them great for Databases ). But when I tried to implement it, I hit
this problem.
Normal B Tree diagrams shows pointers to child nodes which then descend
down to leaves.
But how do I make pointers on the disk? Is it like a file name ?