updated 10:05 pm EST, Tue February 7, 2012
Previous generations of MacBook Air, MBP, iMac
[Update: MacBook Pro eligibility corrected] Apple late today issued further EFI firmware updates to allow previous-generation MacBook Air, MacBook Pro and iMacs to access Lion Internet Recovery, a technology that lets users re-download and reinstall Lion when the hard drive containing the recovery partition has completely failed and no other backup medium is available. The models updated today include the MacBook Air (late 2010), the mid-2010 aluminum iMacs and the mid 2010 MacBook Pros.
The change allows users who have lost the ability to boot from their hard drive or installed a blank new hard drive and don't have a physical backup to restore Lion by re-downloading it from the Mac App Store.
EFI firmware updates require that the computer be connected to external power at all times during the procedure.The machine will restart with a gray screen and a status bar to indicate progress, and must not be powered down or disrupted during this period, which may take several minutes.
The MacBook Air EFI update for models MC504LL/A, MC505LL/A, MC506LL/A, and MC503LL/A is numbered v2.3 and also fixes an issue where the system could restart if the power button is pressed immediately after waking from deep sleep. The update is 2.98MB in size but requires Mac OS X 10.7.3, the latest iteration.
The iMac update for mid-2010 models (MC309xx/A, MC812xx/A, MC813xx/A and MC814xx/A) is a slightly heftier 3.02MB in size and numbered version 1.8. It exists solely to add Lion Recovery via an internet connection to these models. It also requires that 10.7.3 already be installed.
The MacBook Pro EFI update is an update to the one that was issued in late January for the mid-2010 models. It is now at version 2.6 and weighs in at 3.18MB and again requires 10.7.3.
Note: an earlier version of this story misidentified the model affected by the new update due to a typo (still present) on Apple's support website. The MacBook Pro EFI update affects mid-2010 models, not early-2011 models as previously stated.
The relevant updates will automatically appear in Software Update if the user has the machine matching the update. The updates are also available via Apple's support website.