Specifications

Recovery HD
A bootable OS X Utilities volume is installed on a hidden partition (Recovery HD) of the internal drive, and may be used to perform the following tasks:
Repair the internal drive using Disk Utility
Erase or Partition the internal drive using Disk Utility
Restore information on the internal drive using a Time Machine Backup
Restore or Reinstall OS X and Apple applications on the internal drive from the Internet
To boot from Recovery HD:
1. Restart the computer while holding down the Command (Cmd) and R keys. Important: If the OS X Utilities application doesn’t appear after
restarting, restart the computer while holding down the Command (Cmd) Option (alt) and R keys, to access and load the OS X Utilities software
from the Internet. The computer must be connected to a network that has access to the Internet.
2. The OS X Utilities window will appear.
If Recovery HD and Internet access is not available, an external recovery disk may be used. Refer to Apple support article
HT4848.
Some utilities may require an access to the Internet and the Mac App Store.
Serial Numbers
The serial number for iMac (21.5-inch, Late 2012) and iMac (27-inch, Late 2012) is located on the bottom of the stand:
When replacing a stand, use a fine-tip black permanent marker to neatly write the serial number on the bottom of the new stand.
Learning Resources
About firmware updates for Intel-based Macs
About incompatible software (Mac OS X v10.6, OS X Lion, OS X Mountain Lion)
About NVRAM and PRAM
About the SD and SDXC card slot
Boot Camp: Macs that work with 64-bit editions of Microsoft Windows
DVD or CD sharing: Using Remote Disc
EFI and SMC firmware updates for Intel-based Macs
Electrostatic Discharge Precautions and Myths
Hand Tools for Desktop and Portable Repairs
How to clean Apple products
How to identify iMac models
iMac (21.5-inch and 27-inch, Late 2012): Memory specifications
iMac (27-inch, Late 2012): Boot Camp alert with 3TB hard drive
iMac (27-inch, Late 2012): Installing or replacing memory
iMac (Late 2012): External features, ports, and connectors
iMac (Mid 2007) and later models: About startup tones
iMac: Fans run at full speed after computer turns on
Intel-based iMac (Mid 2007) and later: How to find the serial number
Intel-based Macs: Resetting the System Management Controller (SMC)
Isolating issues in Mac OS X
Mac mini (Late 2012) and iMac (Late 2012): About Fusion Drive