Where is the hard disk in the mid 2012 15" Macbook pro with retina I was following various guides for replacing the hard drive. However my mac does not seem to have the standard 2.5" SSD/SATA drive: see this screenshot:



The black rectangular sections are too small to be 'normal' 2.5hdd's as can be seen here when comparing to the SSD:



Does anyone know


what are those rectangular black compartments
how do I swap this (or another smaller?) SSD into the MBPro?
All the black compartments are the Li- Ion Polymer batteries which power your MacBook Pro.    
You won't be able to swap a 2.5'' drive in your Macbook because the Mid 2012 Retina models use a flash memory module.
Here you can see a guide to upgrading the SSD.