Quick–without looking at “About this Mac”–what version of MacOS X are you running?A lot of people have no idea what they have installed, or more importantly, they don’t know that the base operating system can be upgraded. Unfortunately, they often don’t find out until it’s too late.

A brief recent history of Mac OS X: Version 10.4 “Tiger” came out in April 2005 and was refreshed in January 2006 to support the new line of Intel-based systems. Version 10.5 “Leopard” was released in October 2007. Then in August 2009, 10.6 “Snow Leopard” was released. Originally, Snow Leopard was made available as a $29.99 upgrade to Leopard, offering many improvements such as better 64-bit support and a new printing subsystem. Life was good.

Each release of OS X drew a line in the sand, leaving some older systems behind. The Intel version of Tiger did not support the Classic Environment. Leopard did not support the G3 processor and required 512MB of RAM. Snow Leopard dropped support for PowerPC Macs entirely, so if you’re not running an Intel-based Mac, you can’t install Snow Leopard.

Problems can arise when you don’t follow the upgrade path. Based on the number of support calls and e-mails we receive, apparently a lot of people are still running 10.4. Now they are buying iPads and iPod touches that require iTunes 10, but iTunes 10 requires 10.5 or higher. They have a shiny new iOS device they can’t use, and they come to us for help.

On one side, you have the owners of Intel-based systems. The Snow Leopard “upgrade” disc requires that you already have Leopard installed, however Leopard is no longer sold by Apple. For these people, Apple released the Mac Box Set for $129.99, which includes a “full” version of Snow Leopard that can be used to upgrade Tiger. It also includes iLife ’11 and iWork ’09. I’ve heard several people saying that’s too expensive, when the original Snow Leopard release was only $29.99. Bear in mind that past OS X upgrade discs were always $129.99, and the “upgrade” version of Snow Leopard was a “special” for people who had just bought Leopard; you’re also getting iWork (which normally costs $79) for free. So, as long as you have at least 1GB of RAM and an Intel processor, you can use the Box Set to bring your system up to date.

The second group isn’t quite so lucky. They have a PowerPC-based computer running Tiger, but the Box Set only works on an Intel system. The highest release they could install is Leopard, but Apple isn’t selling Leopard anymore. It’s possible to find copies online, but you may end up paying upwards of $180 for a used (illegal or counterfeit) copy. You may also be able to find copies of the Leopard Box Set (Amazon lists used copies starting at $190). I’ve been sending people to eBay or Craigslist, but there’s no guarantee you’ll get a working (or even legal) copy of Leopard.

I’ve heard a suggestion that Apple make OS upgrades available via their new App Store. Good idea, but there are two major flaws in that: First, the App Store is only available if you already have 10.6 installed. Second, the download would require that you burn it to a dual-layer DVD in order to use it, and most of the systems still running Tiger don’t have dual-layer DVD burners installed.

Mac OS X 10.7 “Lion” is supposed to be released later this year. Don’t get caught out in the cold–upgrade early, and upgrade often!

Over the years “we’ve written a lot about Apple’s repair extension programs (REPs)”:http://www.google.com/search?client=safari&rls=en&q=%22repair+extension+program%22+site:blog.smalldog.com&ie=UTF-8&oe=UTF-8. When a particular part failure becomes statistically relevant, Apple will own up to that failure and cover the cost of repair or replacement of that part, generally for three years from the computer’s purchase date regardless of warranty status. It became clear some time ago that a specific set of first-generation style MacBooks (non-unibody) had abnormally high hard drive failure rates. Apple responded by covering the hard drives in these MacBooks.

That repair extension program expired last week. We did so many of these repairs that it seems any qualifying machine has likely been repaired already, so it’s not much of a loss to see the program expire. Apple has five active programs at the moment, and you can read about them “here”:http://www.apple.com/support/exchange_repair/.

The iBook and PowerBook G4 battery program will likely remain in effect indefinitely, as there was a true safety risk with those batteries and there are still plenty of those older machines in active use. There’s also a program to cover specific graphics card issues in some MacBook Pros.

On the accessories side, the very first run of ultracompact USB power adapters can be exchanged for a revised model. You can tell if your adapter qualifies if it does NOT have a chartreuse dot near the prongs and submit your exchange request “here”:http://www.apple.com/support/usbadapter/exchangeprogram/. Finally, some Apple headphones (the kind with the remote right on the wire) can be replaced if the volume changes unexpectedly, controls stop working intermittently, or voice feedback randomly turns on.

It should be noted that many customers believe these programs to be recalls. They are not. The vast majority of products that qualify for these programs do not show symptoms.

There are myriad customization options in Mac OS X–some are in plain sight in System Preferences and elsewhere, while others involve manual editing of plist (property list) files or tricking the system into thinking one file is actually another. One of the most powerful interface tweaks you can make is to the menu bar, and while you can enable menu bar extras through System Preferences and elsewhere, doing so can take some sleuthing.

Mac OS X is built for multiple users. As such, each user has a home folder with that user’s preferences and settings. But there are common resources shared by all users, and these resources are for the most part located in the System and Library folders at the root level of your hard drive. Before I go further, I should note the importance of taking care when modifying anything in either of these folders. One misstep can lead to a completely nonfunctional computer!

The menu bar extras I mentioned before are located at Macintosh HD/System/Library/CoreServices/Menu Extras. All you need to do is drag the files in this folder up to where you’d like them to live in the menu bar. Some of the menu bar extras will not “stick” up there because they are not supported on your system. For example, the ExpressCard menu item will not stick if used on a MacBook without an ExpressCard slot. If you use Mac OS X Server 10.5 or 10.6, you can realize power savings with the CPU menu bar item, which allows you to disable and enable processors or processor cores as more or less power is needed.

Another item in the CoreServices folder is the default desktop picture, which is shown at the login window. You can replace this file with another jpeg of equal resolution and name it DefaultDesktop.jpg to change the desktop picture at the login window.

Your mileage may vary on these hints. Whatever you do, make sure you’ve backed up your computer before trying anything.