Use Monitoring Utilities

Numerous utilities (most of them free) can provide up-to-the-minute vital statistics about your Mac. In most cases, these programs run in the background all the time, but if you prefer, you can 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).


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.

Deciding Which Files to Delete

If you find yourself running desperately low on disk space, it may be time to buy a larger hard drive. In the meantime, you can delete files you no longer need. Begin by repeating the procedure in Clean Out Accumulated Cruft (page 16). If that still leaves you with too little free disk space and you're stuck for ideas, try removing these items:

Cache files: Mac OS X automatically re-creates these files if needed, so feel free to trash the contents of /Library/Caches and ~/Library/Caches.

Downloads: Do you tend to hang onto installers or other downloaded files that you could simply download again if you needed to use them? If so, out they go.

Classic resources: If (and only if) you never use Mac OS X's Classic environment, you can get rid of the Mac OS 9 System Folder (but not the folder named System, which belongs to Mac OS X!) and any Classic applications (usually they are stored in a folder called "Applications (Mac OS 9)").

Developer tools: If you installed Apple's Xcode Tools but aren't developing any software, you can remove the Developer folder located at the top level of your hard disk. The proper way to do this is to double-click the file /Developer/Tools/

Re-rippable music: As a last resort, look in ~/Music/iTunes/iTunes Music for music you still have on CD (and which, therefore, you can reimport). While you're at it, toss out old podcasts you no longer need or can download again for free, as well as any tunes you know you'll never listen to again. Be careful not to trash music you purchased from the iTunes Music Store!

When you're finished deleting files, don't forget to empty the Trash (Finder > Empty Trash) to free up the space formerly occupied by those files.

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.


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.


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 (see Figure 10).

    Figure 10. Activity Monitor, included with Mac OS X, displays CPU and RAM usage, among numerous other statistics.

    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 (, free).

  • App Monitor: If you want to keep an eye on the CPU usage of one application at a time, try App Monitor (, 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 (; $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 (; free, donations accepted).

  • MemoryStick: This simple utility from Matt Neuburg displays a floating bar graph showing your current RAM usage (; 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 (; $10).

  • MenuMeters: My favorite utility of the group, MenuMeters (; free), shown in Figure 11, 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.

    Figure 11. MenuMeters can display RAM and CPU usage, as well as numerous other bits of information, in highly configurable menus.

  • miniStat: For Dashboard fans, this collection of six Dashboard widgets (; free) displays CPU load, free RAM, free disk space, CPU temperature, battery level, and system uptime.

  • iStat pro: Another Dashboard widget, iStat pro (; 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 (; free).

  • ThermographX: This utility (; $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 (; 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.

Real World Mac Maintenance and Backups. Industrial-Strength Techniques
Real World Mac Maintenance and Backups. Industrial-Strength Techniques
Year: 2004
Pages: 144 © 2008-2017.
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