In library we have book register, It contains name of the book and location. Means certain book is present on given location (rack or cupboard)
On rack also some space is allotted to display identification of the rack (the same identification number is referred in register)
You can access the library easily if there is a proper way followed to organize books and you are aware with the same.
The same thing is implemented in computer. Computer knows from smallest addressable unit of the data , how much space is used for address and how much space is used to store actual data.
Use xxd command for more details
