This is part of a series of tips of updating to Mac OS X 10.3 through Mac OS X 10.8 Client. Server versions of Mac OS X are better handled by asking questions in the Server forum.
Backing up your data at least twice is essential. A clone backup, explained in the "backing up" link in the prior sentence, prior to upgrading to Lion will ensure you are able to backstep to Lion in event you don't have a USB Flash drive copy of Lion.
Apple announced Mountain Lion's availability, July 25, 2012.
when you redownload Mountain Lion. It is 4.05 GB which works out to 4147.2 MB, which at 7Mbps or .875 MBps would take 1 hour 19 minutes.
At 1.5 Mbps that would take 6 hours and 8 minutes. At 768 kbps that would take 12 hours and 16 minutes. And that's assuming the traffic at Apple trying to download it isn't overwhelming the servers, and you have a dedicated connection at those speeds. After the download completes, the installer takes 3 minutes before rebooting itself, and 33 minutes after rebooting to complete the installation on an iMac 11,2. Times may vary by speed of the hard drive, connected peripherals (prepherably none), available disc space, and available RAM. Unlike Lion, before the installer begins, it leaves behind a distinct 4.3 GB installer file you can drag to any backup you need before beginning with the 36+ minute installation process.
Mountain Lion, Mac OS X 10.8 has many of the same requirements as Lion, except those listed below:
Apple has the system requirements for Mountain Lion, based on their annual time schedule of model releases on http://www.apple.com/osx/specs/
Below are others means of identifying the compatibility if you completely read this tip.
At this point several places on the Net already are claiming Mountain Lion compatibility for certain software or hardware that is non-Apple.
Any announcements of Mountain Lion compatibility prior to July 25, 2012 should be treated with skepticism, and tested on a backed up system
prior to updating those entries on the Net and getting Mountain Lion either from an authorized reseller or Apple. Note: at the point of writing this
tip, no USB Flash drive is available for Mountain Lion, and it can only be gotten from Apple Mac App Store. Stay tuned!
Macs sold with different hardware in the same model name on or after July 25, 2012, may not be able to run Lion, or earlier versions of Mac OS X,
though are still able to run Windows. An older Mac may be needed to run software not yet tested with Mountain Lion. See below for resources on telling a Mac's age.
Someone who does not have the serial number of their machine due to a logicboard replacement,
or other is desiring to purchase an older machine and wanting to know about Mountain Lion's compatibility,
will benefit by the following. The model identifier, also known as Machine ID, can be found in Apple menu -> About This Mac -> System Information or More info. The following Macs with 10.6.8 or later, 2GB of RAM, and 8 GB of hard space (presumably an additional 15% of free hard disk space will be beneficial as has always arbitrarily been found in the past) are able to upgrade to Mac OS X 10.8:
iMac 7,1 and later
MacBook 5,1 and later
MacBook Pro 3,1 and later
MacBook Air 2,1 and later
Mac Mini 3,1 and later.
Airdrop is compatible on 10.8 systems of the following model identifier:
MacBook Pro 5,1 and later
MacBook Air 3,1 and later
MacBook 5,1 and later
iMac 9,1 and later
Mac Mini 4,1 and later
Mac Pro 4,1 and later
Airplay mirroring is compatible on 10.8 systems of the following model identifier:
Mac Mini 5,1
MacBook Air 4,1
MacBook Pro 8,1
....Mac Pro...noticeably absent in spite of June 11, 2012's new release. If someone getting a new Mac Pro would care to comment, please feel free to.
A similar feature is available to older Macs through third party software and hardware listed on this tip.
Powernap is compatible just with these Macs:
MacBook Air 3,1
MacBook Pro 10,1 and later.
A very good third party resource for identifying older Macs is on EveryMac.
Tips present for Lion's release are fairly good for Mountain Lion as far as is known as of the date of this tip's posting.
People buying new Macs as of June 11, 2012, also qualify for the up to date program. If you should choose to go this path, be sure to backup your data at least twice before installing the up to date program installation, if you want a chance to revert in event some application is Lion compatible and not Mountain Lion compatible. Apple has a history of making Macs only compatible with the operating system available at the time of their refresh date.