10 essential tasks to keep Mac OS X Leopard purring

One of the big selling points for Mac OS X Leopard is that it is a stable operating system that is not prone to crashes, freezes, corrupted or fragmented hard drives, viruses and spyware, or the seemingly inexplicable performance losses typically associated with Windows. Overall, Leopard lives up to its reputation of simply working, without the need for a litany of maintenance routines and utilities to keep it going.

However, even the best-engineered car still requires the occasional oil change and tune-up to keep it running at its best. Periodically performing a few key maintenance tasks can keep Leopard -- and earlier versions of Mac OS X -- running strong and prevent or resolve problems.

1. Keep your software up to date

One of the easiest (but often overlooked) ways to keep any computer running at its best is to ensure that it is running up-to-date versions of both its operating system and any installed applications. Updates typically add new features, fix bugs, and/or patch security holes that leave the system vulnerable to viruses or other forms of attack.

While new features are usually reason enough to check for software updates, the bigger advantages in keeping your system running optimally are in the bug fixes and security patches, as both of these typically yield a faster, more stable and more secure environment.

Apple's Software Update feature provides an easy-to-use interface for updating both Mac OS X and any Apple-branded applications, such as the iLife and iWork suites. By default, Software Update is enabled and will check for updates on a weekly basis.

However, you should also keep an eye on any third-party apps or system components that you have installed. Most programs include some type of built-in mechanism for checking for updates, such as the Microsoft Auto Update utility that comes with Office or an option in an application's preferences that tells it to check for updates whenever it's launched.

Sites like MacUpdate and VersionTracker are useful allies in ensuring all your software is up to date (as well as in helping you find new applications). If you have a large number of applications for which to manage updates, VersionTracker also offers a subscription service and utility as well as a Dashboard widget to help ensure that your apps are up to date.

While software updates are generally solid, some updates from both Apple and third-party developers have been known to create their own set of problems -- sometimes even removing or altering the functionality of the software. These problem updates are typically pulled from the Internet quickly, often replaced by newer updates that correct the problem.

For these reasons, not installing updates immediately when they are released can be a good habit to get into. It's wise to keep track of new updates as they appear, but try waiting for a day or two to see if any problems are reported on Mac news and information sites such as MacNN, MacDailyNews, Ars Technica's Apple section and Apple's own discussion forums before proceeding with the installation.

When you receive a Software Update notification, you can elect not to install specific updates. In the Software Update pane in System Preferences, you can also disable automatic checking of updates or change the feature to check on a monthly rather than weekly basis. If you disable automatic checking altogether, be sure to run Software Update manually (choose the Software Update command in the Apple menu) on a periodic basis or in response to news that specific updates have been released.

2. Make sure your hard drive is healthy

There was a time (before the release of Mac OS X) when Mac users religiously ran Disk Utility or an alternate hard drive utility at least once a month to verify the integrity of their hard drive directory structures.

A hard drive's directory structures are created when a disk is formatted or partitioned; they're essentially a map of the drive's magnetic platters. They translate the physical sectors that store bits of data on a drive to usable space for files, applications and Mac OS X system components. If they become damaged or corrupted, the Mac can have a tough time locating pieces of files as needed to accomplish tasks like opening files, launching applications and even booting up.

The good news is that technology has come a long way since the days when Disk Utility was a frequent necessity. The default file system for Leopard is Mac OS Extended Journaled, or HFS+J. Journaled file systems keep a transaction log of changes to data on the hard drive. (Microsoft Corp.'s NTFS is another example.) Should the hard drive experience a problem like an unexpected reboot or removal without being ejected properly -- the two most common causes of damage to directory structures -- the file system can rely on the transaction log to repair the damage.

Even so, hard drives can develop some directory corruption over time, particularly if a hard drive is repeatedly unplugged or removed without being properly ejected or if the drive is formatted using an older nonjournaled file system such as the Mac OS or Mac OS Extended file systems, also known as HFS and HFS+, respectively.

So it's still a good idea to use a disk utility occasionally, especially whenever you experience unexplained problems, crashes or failures to open items. If you have drives that aren't journaled, you should still do this on a regular (close to monthly) basis. Journaled drives, however, can be checked less frequently. You can try Disk Utility's Verify Disk and Repair Disk features or a third-party utility such as Micromat's TechTool Pro, Prosoft's Drive Genius, or Alsoft's DiskWarrior, all of which cost around US$100.

These tools essentially work by comparing a drive's directory with its actual contents , also called verifying or examining the disk. If problems are found, the utilities can attempt to repair the directory.

The extent to which they are successful depends on the format of the disk, the extent of the damage and the utility being used. In general, third-party utilities tend to be somewhat more successful than Disk Utility in recovering severely damaged directories, though your mileage may vary.

Generally, Disk Utility (found in /Applications/Utilities) is the first stop for checking for hard drive issues because it is freely available and relatively easy to use for identifying and resolving most problems. To verify or repair a drive's directory structures, select the drive from Disk Utility's list box, click the First Aid tab, and click the Verify Disk or Repair Disk button.

When you repair a disk, Disk Utility will first verify the disk and then attempt to repair the directory information if it finds problems.

Note: If you are comfortable working from the command line, you can also boot a Mac into single-user mode and use the Unix fsck command, though this is more commonly used as a troubleshooting option if a Mac's hard drive is so corrupted that it can't boot successfully.

The same functionality is available in Disk Utility, which is generally easier and safer for many users, as fsck 's options and single-user mode provide unrestricted access to a Mac's file system.

Then there are the physical components to any hard drive. These include the spinning magnetic disks (known as platters) that hold data, the read/write heads that scan and access those platters, the drive motors, the cache RAM chips that speed up data access, and the chips that tell the drive how to function and interact with the other components of a computer. A failure in any of these physical components can lead to problems much more serious than disk directory problems.

Almost all modern hard drives include a technology known as Self Monitoring and Reporting Technology, or SMART. SMART allows hard drives to continuously check, diagnose and report the state of their physical components. While SMART status information won't prevent a hard drive from failing, primarily because such a failure is a physical problem with the hardware rather than corruption of directory data, it can alert you to problems before they become so severe that you can no longer access the hard drive.

Most hard drive utilities allow you to view a drive's SMART status. In Disk Utility, the SMART status is listed along with general information about a disk at the bottom right of the window. (Note: To view the SMART status of a drive, you need to select the drive itself rather than a volume that exists on the drive.) ISlayer.com's free iStat Pro and iStat Menus show you SMART status and other system information from the Dashboard or the Mac's menu bar.

If a drive's SMART status says Verified, the drive is healthy. If the status is About to Fail or Failed, you should immediately back up all data and replace the drive.

3. Don't overfill your hard drive

Today's Macs serve as a hub for all kinds of digital media content, whether you've produced it yourself, purchased it from the iTunes Store, or ripped it from your CD and DVD collection. All of those videos, photos and songs can fill a Mac's hard drive pretty quickly. Which brings us to another way to keep Leopard running smoothly -- don't overfill a Mac's hard drive.

Like other operating systems, Leopard uses the hard drive to store not only your data, but also various temporary and cache files needed to support the data and run applications properly. It also relies on the hard drive for virtual memory, in which data not in active use gets swapped out of RAM to the hard drive to accommodate active applications. Leopard invisibly performs these functions without any intervention from the user.

However, in order for this to happen, there has to be free space on the hard drive for Leopard to use. If the hard drive is too full, Leopard has to rely on the start-up drive for these purposes, which means the Mac's performance will seriously degrade. In some cases, you may even notice some erratic behavior and application crashes if the hard drive is almost completely full.

That's why being aware of the free space on your hard drive is important in keeping your Mac functioning at its best. A good rule of thumb is to make sure that you have at least 10% of your drive free at any given time. You can see a drive's free space at the bottom of any Finder window for a folder that resides on the drive (or for the drive itself).

If your drive begins to get too full, you have a few options. The simplest solution is to buy an external hard drive. With a laptop, you'll want to move larger or infrequently used files to the external drive; with a desktop system you can simply make it a second hard drive for regular use. You can also replace the internal hard drive of either a desktop or portable Mac with a larger drive.

Finally, you could try to trim the amount of data on your current drive. Disk Inventory X (free) and id-design's WhatSize (shareware, $13) are two helpful tools for discovering just what files are eating up hard drive space and which can be easily moved to a secondary drive or potentially deleted altogether. Prosoft's $99 Drive Genius, which offers several hard drive tools in a single application, now includes a DriveSlim feature that can search for large files, files that have not been accessed recently and duplicate files.

Note: This same rule applies to the embedded version of Mac OS X that powers both the iPhone and the iPod Touch. If you notice erratic behavior on those devices and they are filled to bursting, removing some content may help (though there could be other causes as well).

4. Delete cache files

Many applications rely on cache files to improve performance. The most obvious example is Web browsers, which cache images and other content from Web servers to speed up repeated access to the same files. Leopard itself maintains a series of cache files for improving system performance when using a number of features.

Cache files can present problems if they become corrupted or damaged. The operating system or an application that relies on the cached data may behave erratically or crash because it can't properly read the data in the file -- leading to potentially more corruption if an app crashes while it's writing to the file.

Unlike files in the Unix /tmp directory, cache files aren't cleared when a Mac is rebooted, which means that even when they aren't corrupted, cache files can sit around taking up space on your hard drive long after a given application is deleted. They can also retain settings and private information that you may wish to get rid of. As such, pruning cache files is a prudent choice, particularly if you notice that an application isn't as stable as it used to be.

Cache files exist for both the system (in the /Library/Caches folder at the root level of a start-up drive) and for each user (in the same location inside each user's home folder). Since cache files are not used to store application preferences or general settings, you can safely delete them without losing any data, and they will be regenerated as needed.

5. Verify and delete preferences files

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