As you use your computer, your files gradually become fragmented into smaller segments scattered across your disk. Some people consider this a serious problem and go to great lengths (and expense) to correct it. Before worrying about fragmentation, you should understand how and why it happensand what the real-world consequences are.
Pretend, for the sake of illustration, that your hard disk consists of exactly ten blocks, and that initially, your disk contains five small files (A, B, C, D, and E), each of which takes up exactly one block. Your disk looks tidy and clean, something like this: ABCDE_____.
If you delete files B and D and add a couple of new files, F and G, your disk looks like this: A_C_EFG___. If you then add a file H that's twice as big as the others, the drive puts it at the end, like so: A_C_EFGHH_. Now let's say file G grows to two blocks in size. There being too little space between F and H, G must split into two segments: A_C_EFGHHG. Finally, if you add file I and delete file F, your disk looks like this: AIC_E_GHHG.
Are you with me so far? Now imagine this happening with hundreds of thousands of files of many different sizes. Some tiny files might occupy just one block, while some huge ones may occupy millions of blocks. The more you read and write files, the more jumbled the data becomes: individual files split into numerous noncontiguous chunks, and lots of small, empty spots where other files once lived. That's fragmentation: the normal state of your hard disk!
Ordinarily, you never notice fragmentation, because Mac OS X keeps track of which parts of which files are where, and automatically reassembles or disassembles them as needed. With modern hard drives, this process is so fast that it's normally imperceptible. Furthermore, starting with Panther, Mac OS X included automatic background defragmentation of smaller (<20 MB) files, so that although files may not be contiguous with each other, at least most of them are in one piece.
The problem occurs when you have programs that must read or write massive amounts of information in real time, such as audio or video recording and editing applications. When these large files become fragmented, the drive's read-write head must physically zip back and forth over the disk to get all the segments, and sometimes the rate at which it does the zipping is too slow to keep up with the amount of data coming in (or going out). The results can include gaps in the data, stuttering, or slow application performance.
For ordinary users, defragmentation is a waste of time unless the fragmentation is extraordinarily severe (as evidenced by long delays in opening and saving files). But if you use high-end audio or video applications regularly, occasional (say, monthly) defragmentation is worthwhile. Several utilities pick up where Mac OS X leaves off, performing thorough defragmentation and making sure all the empty space on the disk is contiguous, in order to squeeze every last bit of performance out of your drive. The process is quite slow, howeverand if you're defragmenting large disks, your computer could be effectively out of commission for many hours. I recommend letting the process run overnight (or better yet, over a weekend). Defragmentation is also somewhat risky, since it involves deleting and rewriting almost every file on your drive. A good backup is always essential before undertaking defragmentation.

Note
Related to defragmentation is optimization, which means moving the most frequently used files to the portions of the disk that can be accessed most quickly. Most utilities that defragment also optimize.

Utilities that perform defragmentation include:

• Disk Defrag, part of SpeedTools Utilities (www.speedtools.com; $100)
• Drive Genius (www.prosofteng.com; $100)
• iDefrag (www.coriolis-systems.com; $30)
• TechTool Pro (www.micromat.com; $98)

Tip
Another way to defragment your disk is to make a complete, bootable copy (a clone) onto another hard disk, erase the original disk, and then reverse the process, cloning the backup disk onto the original. When the computer writes data to an empty drive, it automatically makes all the files contiguous.
Note that you cannot make a bootable clone simply by dragging files onto another drive. You must use a utility designed to do that job, such as SuperDuper! (www.shirt-pocket.com; $28), Carbon Copy Cloner (www.bombich.com/software/ccc.html; free, donations accepted), or most full-featured backup programs.

When Apple Releases a New Version of Mac OS X

Every 18 months or so, Apple rolls out a new, major update to Mac OS X. In anticipation a major update, I'd like to share some advice you should follow whenever Apple releases a major new version of Mac OS X.

Note
Even more important than the major upgrades is keeping current with minor updates to Mac OS X, because these are likely to fix serious bugs and security holes. For more information, read Install the Latest Version of Mac OS X and Use Software Update to Install Apple Software Updates.

Buy It!

For the past several years, Apple has consistently charged $129 for major Mac OS X upgrades. As much as we might all wish they were less expensive, I recommend adding that amount to your budget right now; ultimately, you'll get much more than your money's worth. Major upgrades invariably contain features that enable you to get more done in less time and with less effort. If time is money, upgrades pay for themselves. So plan to make that investment, and it won't seem like such a big deal when the time comes

Buy Take Control of Upgrading

I write this article based on weeks of extensive testing and dozens of installations of the new operating system on numerous test machines. (I've written Take Control of Upgrading to Panther and Take Control of Upgrading to Tiger so far, and I plan to continue the string with Take Control of Upgrading to Leopard and all the rest of Apple's big cats in the future.)
But you're already spending $129 on the operating system itself, so why should you pay even more for an ebook about how to install it? Isn't it just a matter of popping in a DVD and clicking a button. If only it were so. Every upgrade of Mac OS X brings with it not just new features and bug fixes but brand-new hardware and software incompatibilities, installer oddities, and confusing custom installation options.

Make a Fresh Bootable Backup

Before performing any major system upgrade, be sure to make a new, fresh duplicate of your startup drive (even if you regularly make duplicates once a week). In fact, resources permitting, make two. System upgrades can cause many things to go wrong, and you'll appreciate the security of knowing you can restore your system to its previous state if a problem occurs

Upgrade

You may be surprised how often someone purchases a Mac OS X upgrade, reads about the installation process, and then leaves the DVD in a drawer for months. Some people habitually wait until the first or second minor update after a major Mac OS X release before taking the plunge, whether to give Apple time to work out all the bugs, to give developers time to update their applications for compatibility, or to see how other people like it before committing themselves. And others feel nervous about upgrading until it's nearly time for the next major version to be released! Don't let this happen to you.
I'm an early adopter, and although I've experienced my share of minor hurdles, I've never regretted a decision to upgrade immediately. You may, however, wish to delay an upgrade if you're in the middle of a project and can't afford any downtime, if you rely heavily on an application that has not yet been updated to work under the new system, or if you expect to buy a new Mac in the near future (which will, of course, include the latest version of Mac OS X).
8. Monitor Your Mac's Health
No matter how diligently you perform the maintenance tasks I recommend in this article, you won't truly know how well (or how poorly) your Mac is running unless you make the effort to find out. The fact that no smoke is billowing from your SuperDrive is a good sign, of course, but it's hardly definitive proof that all is well. In this article, I show you how to find out what's going on under the hood.

Use Monitoring Utilities

run them manually when you get curious about your Mac's current state. I provide a list of several such utilities just ahead. But first, you should understand what information you might want to monitor and why.

RAM Usage

Mac OS X manages your computer's RAM efficiently for the most part. Applications can dynamically adjust the amount of memory they use, and even if all your RAM is actively in use, a virtual memory system lets Mac OS X use a portion of your hard disk to extend your RAM, automatically swapping (or "paging") data between the disk and the physical RAM as needed.
Even so, if you have enough applications open at once, and if they require enough memory to perform their respective tasks, you can get to a point where the data swapping occurs constantly. This slows everything on your Mac way down, and it also uses up disk space.
You should also be aware of a type of bug known as a memory leak. Applications usually ask the system for a certain amount of memory for any given task and then give it back when they're done with it. But sometimes, due to a programming error, an application keeps taking memory and not returning any, so that by doing nothing more than staying open, it constantly chews up more and more RAM. You can recover the used memory simply by quitting the applicationbut you might never know you have this problem in the first place without monitoring your RAM usage.
For all these reasons, I recommend keeping an eye on how much RAM is currently in use. If the free RAM drops near zero, consider closing windows, quitting applications, or even restarting your machine to reduce your Mac's dependence on virtual memory. Better yet, add more RAM (if possible).

Note
In Mac OS X, RAM is not simply "used" or "free" but can be used in any of three different ways: wired (in use and crucial to keep your Mac running); active (in use now, but may be paged out to disk later); or inactive (not currently in use, and possibly paged out to disk, but also stored in RAM for fast access when needed). Most RAM-monitoring utilities break down RAM into these three categories plus "free," and generally include documentation that explains RAM usage in greater detail.

Disk Usage

With hard disk capacity constantly on the rise, you're now less likely to run out of space than you were a few years ago. Nevertheless, the consequences of running out of space can be severe. For one thing, as your hard disk approaches its maximum capacity, your Mac may run more slowly as files become increasingly fragmented. Worse, you could lose data, because your Mac has no space to save a file. And even more seriously, your computer may hang, crash, or fail to start up if it runs out of physical RAM and runs out of disk space to use for virtual memory.
In general, I recommend leaving at least 10 to 15 percent of your hard disk space empty to provide breathing room for file storage, virtual memory, disk image creation, and other tasks. When your disk gets close to that level, delete any unneeded files (see the sidebar below for advice about what files to delete), and archive seldom-used files to CD, DVD, or an external hard drive.

Although you can tell how much free space is on a disk by selecting it in the Finder and choosing File > Get Info, you may not notice if it gets dangerously full while you're busy working. (Mac OS X does display a warning message when space gets critically low, but it appears much too late for my taste.) Several utilities display a live status indicator (in your menu bar, a Dock icon, or a floating window) showing your disks' current free space.

CPU Load

Your Mac contains one or more CPUschips that do the bulk of the computer's information processing. Depending on what software is running and what that software is doing, the CPU load goes up and down. Because all your applications share the available CPU power, it's generally true that the higher the overall load, the slower your software will run. In addition, greater CPU load means a higher internal temperature, forcing your computer's fans to work harder.
Having your CPU(s) run at 100 percent capacity from time to time is normal. However, if the load is always at or near maximumor if it's high even when your computer is relatively inactiveyou may have a problem. For example, a background application could have a bug that causes it to use too much processor capacity, slowing down your foreground tasks. Or you may be running more applications than your hardware can handle gracefully. In any case, keeping an eye on CPU usage can help you spot potential problems before they get out of hand. Some CPU monitoring tools display a breakdown of usage by application, so that if one program is hogging too much of the CPU capacity, you can force it to quit.

Temperatures

Extreme heat can damage delicate components inside your Mac. This is why all Macs have carefully designed cooling systems, which usually rely on two or more fans to vent heat away from the processor, hard drive, and other vital components. These fans, in turn, rely on one or more internal temperature sensors that tell them when to turn on or off or to increase or decrease speed.
If a fan malfunctions, if dust blocks the flow of air through your computer, or if a defect in your computer causes it to overheat for some reason, bad things can happen. Your Mac may hang, shut down unexpectedly, or display other improper behavior. Depending on the nature and severity of the problem, you might be looking at an intermittent inconvenience or an expensive trip to the repair shop. In any case, it behooves you to be alert to excessive temperatures.
Several utilities monitor each of your computer's internal temperature sensors, so that you can easily see when heat exceeds safe limits and take action before damage occurs.

Note
The types, positions, and design of temperature sensors vary from one Mac model to the next. Not all Macs' sensors work with monitoring utilities or provide live updates of their readings.

Other Statistics

Some utilities monitor other statistics that may be interesting (though not necessarily relevant to your Mac's health). These include:

• Network traffic
• Disk access activity
• Battery level (for portables)
• System uptime (time since the computer was last turned on or restarted)

Monitoring Utilities

Although this is by no means an exhaustive list, the following utilities all provide one or more monitoring services:

• Activity Monitor: This utility, included as part of Mac OS X (in /Applications/Utilities) displays CPU load, RAM usage, disk activity and usage, and network traffic
• Activity Monitor also displays memory and CPU usage statistics for each running application, and enables you to quit individual applications. Although it includes an optional floating CPU window, Activity Monitor is not the best choice for background operation.
• Amnesia: This tiny application displays current CPU load and free memory (only) in its Dock icon (http://dockapp-osx.sourceforge.net/dockapps.html, free).
• App Monitor: If you want to keep an eye on the CPU usage of one application at a time, try App Monitor (http://blazingmousesoft.free.fr/, free), which displays a customizable usage graph in either a window or a Dock icon.
• Hardware Monitor: This utility can display a wide variety of statistics in your menu bar, a Dock icon, or several other formats. Information includes heat sensor readings, power supply voltage and current, fan speeds (in RPM), battery level, and other data, depending on your Mac model (www.bresink.com/osx/HardwareMonitor.html; $7).
• Mac HelpMate: In addition to performing many maintenance tasks, this utility displays free RAM, internal temperature readings, disk usage, S.M.A.R.T. status, and system uptime (www.macworkshops.com/machelpmate/; free, donations accepted).
• MemoryStick: This simple utility from Matt Neuburg displays a floating bar graph showing your current RAM usage (www.tidbits.com/matt/; free).
• Memory Usage Getter: Somewhat along the lines of Activity Monitor, this utility displays overall RAM usage, plus per-application RAM and CPU usage, and enables you to quit individual applications (http://homepage.mac.com/simx/; $10).
• MenuMeters: My favorite utility of the group, MenuMeters (www.ragingmenace.com; free), adds tiny, customizable indicators to your menu bar to display any or all of the following: CPU load, RAM usage, disk access activity (with usage on a drop-down menu), and network traffic.
• miniStat: For Dashboard fans, this collection of six Dashboard widgets (http://shockwidgets.com/; free) displays CPU load, free RAM, free disk space, CPU temperature, battery level, and system uptime.
• iStat pro: Another Dashboard widget, iStat pro (www.islayer.net; free) displays a single panel with the following information: CPU load, RAM usage, network traffic (and bandwidth), disk usage, battery level, and system uptime.
• Temperature Monitor: This utility displays readings from your Mac's internal heat sensors, and even produces a graph of the temperatures over time (www.bresink.com/osx/TemperatureMonitor.html; free).
• ThermographX: This utility (www.kezer.net/thermographx.html; $7) displays the readings of all internal heat sensors in your Mac and even keeps a graph of the temperature over time. But it's not compatible with every Mac model.
• X Resource Graph: XRG (www.gauchosoft.com; free) provides highly customizable graphs of CPU usage, RAM usage, disk access activity, network traffic, internal heat sensors (up to three), and battery level, plus weather (in a city of your choice) and stock market data