System maintenance under Mac OS X is much simpler than it ever was under Mac OS 9. In the bad old days, even commercial utilities didn’t always restore your ailing Mac to health. Don’t even get me started on extension conflicts.

OS X eradicated most of the previous system’s headaches just by virtue of its completely new, UNIX-based architecture. But even OS X can get sluggish over time, or have the occasional oddly behaving program. That’s why it’s still a good idea for Mac users to run certain basic maintenance routines from time to time.

Without going into the technical details, suffice it to say that these maintenance routines “clear out the cobwebs” and return your Mac to its usual efficient state. While Apple provides ways to perform many of these tasks, it never bothered to consolidate them in one handy utility. But plenty of others have.

Generally speaking, what third-party Mac OS X maintenance utilities do is take what are essentially UNIX text commands and put them in a visually more accessible form with clickable buttons and drop-down menus. I have tried several such utilities, including Socks and Cocktail. All have their merits, but one, OnyX, stands above the others for one simple reason: it’s free. (Both Socks and Cocktail are $15 shareware, but free is free.)

Like others of its ilk, OnyX provides a handy way to repair disk permissions, run Unix system maintenance scripts, run prebinding and optimization operations, and delete log and cache files. If you don’t understand a word of what you just read, that’s OK. You only need to know that running these routines periodically helps keep your Mac in optimum condition.

Another thing to like about utilities like OnyX is that they open access to features and options hidden in Mac OS X. (Why Apple doesn’t provide access to these features in the SystemPreferences is a mystery.) In OnyX, clicking on the Parameters icon brings up a whole collection of system options in seven categories, including Finder, Dashboard and Exposé, Dock and Safari.

Some examples of what you can change:

• In the General category, you can elect to have double scroll arrows at both the top and bottom of all your Finder windows.

• A menu (also in the General category) to choose the format of files saved when you use OS X’s built in screen capture function. The default is a PNG file, which can be converted to other formats via the Preview software Apple supplies with all Macs, but what if you want all your screen grabs in JPEG format? OnyX not only lets you change the default to one of 10 image formats, it lets you change the default name.

• In the Dock section you get a third option, “Suck,” for the Minimize window effect. You can also anchor the Dock to the top of the screen, though I can’t imagine why you’d want to.

• With OnyX, you can disable Dashboard (Apple provides no option for turning it off). If you change your mind, you can always use OnyX (or one of the other third party utilities, for that matter) to re-enable it. But it’s nice to have the ability to choose.

While utilities like OnyX draw the most interest from geeks who relish tweaking and optimizing their Macs, I think many less technically inclined users could derive some benefits. If nothing else, you can use it to make sure all of OS X’s UNIX maintenance routines have run (yes, I know Tiger OS X 10.4 is supposed to do this automatically, but I still prefer to run the routines manually sometimes. It can’t hurt.)

And you very well could find a system preference that you were dying to change but could never figure out how.