What You Should Know Before Installing Mac OS X

Compatible Versions & Installation Discs

Each major version of Mac OS X (the “tenth” of a point system, meaning 10.6, not 10.6.1) brings new system requirements with it. Generally, you cannot install a version of Mac OS X that is older than the original version that came with your computer. If you bought a Mac Pro that originally shipped with 10.5.6, you cannot install 10.4, and it is unlikely that even 10.5.5 works properly, if at all, on that machine. In fact, some Macs have shipped with specialized versions of Mac OS X. For example, that Mac Pro that shipped with 10.5.6 may have additional drivers to work with hardware that did not exist the day that 10.5.6 originally debuted. Because of this, you should not install Mac OS X from a retail disc unless the version on the disk is newer than the version that is on your restore disc. The Mac Pro owner could only install from a retail disc that has 10.5.7 or later on it. To install 10.5.6, she should use her original restore disc.

There are other important differences between retail and restore discs. Restore discs, which can be CDs or DVDs, are bundled inside your Mac’s box. Apple designs these discs to work with the computer they ship with; using these discs, you may be able to install Mac OS X onto a different computer, but even if the installer lets you do this, you may end up with an erratically behaving machine. Use improper restore discs at your own peril. (Of course, if your computer originally shipped with Mac OS X 10.7 Lion or later, you don’t even get a disc.)

Retail versions of Mac OS X have typically contained only the operating system itself. This means it does not include iLife, iWork, or other software Apple may have bundled with your Mac. Restore discs, on the other hand, usually include these applications on the discs. When you reinstall Mac OS X with a restore disc, you have the option of reinstalling those applications, too. Finally, it is worth noting that the Apple Hardware Test only comes on a restore disc and is only guaranteed to work with your Mac model.
System Requirements

Here are the minimum requirements for each version of Mac OS X. Remember that your Mac cannot use a version of Mac OS X that is older than the version that originally came with the machine. The absolute earliest version of Mac OS X appearing in an Intel Mac is 10.4.4, which shipped with the first Intel iMacs. PowerPC support ended with the 10.5 family, and PowerPC G3 support ended with the 10.4 family. Finally, Mac OS X 10.4 is the last major version of Mac OS X that allows you to run the Classic Mac OS 9 environment. Only PowerPC-based machines support this feature.

  • 10.8: Specific Mac models (see http://support.apple.com/kb/HT5444 for more details), 2GB RAM, 8GB hard drive space, and Mac OS X 10.6.8 or later already installed (if upgrading).
  • 10.7: Intel Core 2 Duo processor or later, 2GB RAM, 7GB hard drive space, and Mac OS X 10.6.6 or later already installed (if upgrading).
  • 10.6: Intel processor; 1GB RAM; 5GB hard drive space.
  • 10.5: Intel processor or PowerPC G5 or G4 (867Mhz or faster); 512MB RAM; 9GB hard drive space.
  • 10.4: PowerPC G3 Mac with built-in FireWire; 256MB RAM; 3GB hard drive space.
  • 10.3: PowerPC G3 with built-in USB; 128MB RAM; 3GB hard drive space.
  • 10.2: PowerPC G3 (excluding the original PowerBook G3, aka “Kanga”); 128MB RAM; 3GB hard drive space.
  • 10.0 & 10.1: PowerPC G3 (excluding the original PowerBook G3, aka “Kanga”); 128MB RAM; 1.5GB hard drive space.

Worthwhile Precautions and Preparations

Apple has gone to great lengths to make the installation or upgrade of Mac OS X as trouble-free as possible. If you want to be certain that you have done everything in your power to prepare your Mac for the upgrade, performing these six tasks should be enough:

  • Verify that your Mac meets or exceeds the minimum requirements for the version of Mac OS X you are about to install. If you are re-installing the original version that came with your Mac, this is a non-issue.Check to see if there are any available firmware updates for your computer, and if so, install them before you install Mac OS X.
  • Software Update finds firmware updates for all Intel-based Macs and many PowerPC-based Macs. For G3 and early G4 PowerMac computers (or for the perfectionists), visit Apple’s support site and search the Downloads section for firmware updates for your Mac model. There may be firmware updates that you must manually download and install.
  • Disconnect all peripherals (excluding Apple-branded mice and keyboards) from your computer before rebooting with your install disc. If you are performing a remote installation via Ethernet, you may leave that cable plugged in.
  • If you are running Mac OS X 10.5 Leopard, you may know that Software Update can download Apple updates in the background and install them when you restart your computer. If you are going to upgrade to Snow Leopard, make sure that you install all downloaded updates before booting from the Snow Leopard install disc. You do not need to install updates your computer has not yet downloaded.
  • Back up your data! Because you only need one copy of those priceless photos, right?
  • Finally, Disk Utility can be your best friend when it comes to preventing installation nightmares. While booted from your hard drive, repair disk permissions on your Mac OS X volume.
  • Then, when you boot from the Mac OS X install/restore disc, verify (and repair, if necessary) your Mac OS X volume in Disk Utility before beginning the Mac OS X installation. (You can find Disk Utility in the Utilities menu list once you have booted from the install disc).