Editor’s Note: The following article is an excerpt from
Take Control of Maintaining Your Mac, a $10 electronic book available for download from
TidBits Electronic Publishing. The 86-page ebook provides complete details of maintenance tasks you should perform daily, weekly, monthly, and yearly, and how to prepare for Mac OS X updates.
No matter how diligently you perform the maintenance tasks I recommend in the
Take Control of Maintaining Your Mac
ebook, 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. Here’s how to find out what’s going on under the hood.
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.
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
. 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 application—but 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 Mac to reduce your 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:
(in use and crucial to keep your Mac running);
(in use now, but may be paged out to disk later); or
(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.
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
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 unneeded files (see the
“Deciding Which Files to Delete” section
on the next page), 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.
Your Mac contains one or more CPUs—chips 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 maximum—or if it’s high even when your computer is relatively inactive—you 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.
Some utilities monitor other statistics that may be interesting (though not necessarily relevant to your Mac’s health). These include:
Disk access activity
Battery level (for portables)
System uptime (time since the computer was last turned on or restarted)
Deciding which files to delete
If you’re 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. Another section of this ebook offers some suggestions on deleting unnecessary files, applications, and widgets. But if you’re still left with too little free space and you’re stuck for ideas, try removing these items:
Cache files: Mac OS X automatically re-creates these if needed, so feel free to trash the contents of /Library/Caches and ~/Library/Caches.
Downloads: Do you hang onto installers or other downloaded files that you could simply download again if needed? 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 Classic applications (usually stored in a folder called “Applications (Mac OS 9)”).
Developer tools: If you installed Apple’s Xcode Tools but aren’t developing any software, remove the Developer folder at the top level of your hard disk. The proper way to do this is to double-click the file
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). 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 this is by no means an exhaustive list, the following utilities all provide one or more monitoring services:
Activity Monitor, included with Mac OS X, displays CPU and RAM usage, among numerous other statistics.
• 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
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, which displays a customizable usage graph in either a window or a Dock icon (free).
• Hardware Monitor: This
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
displays free RAM, internal temperature readings, disk usage, S.M.A.R.T. status, and system uptime (free; donations accepted).
• MemoryStick: This
from Take Control’s own Matt Neuburg displays a floating bar graph showing your current RAM usage (free).
• Memory Usage Getter: Somewhat like Activity Monitor, this
displays overall RAM usage, plus per-application RAM and CPU usage, and enables you to quit individual applications ($10).
MenuMeters can display RAM and CPU usage, as well as numerous other bits of information, in highly configurable menus.
• MenuMeters: My favorite of the group,
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 (free).
• miniStat: For Dashboard fans, this
collection of six widgets
displays CPU load, free RAM, free disk space, CPU temperature, battery level, and system uptime (free).
• SysStat: Another Dashboard widget,
displays a single panel with the following information: CPU load, RAM usage, network traffic (and bandwidth), disk usage, battery level, and system uptime (free).
• Temperature Monitor: This
displays readings from your Mac’s internal heat sensors, and even produces a graph of the temperatures over time (free).
• ThermographX: This
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 ($7).
• X Resource Graph:
provides highly customizable graphs of CPU usage, RAM usage, disk access activity, network traffic, internal heat sensors (up to three), and battery level, plus the weather (in a city of your choice) and even stock market data (free).
Check your drives’ S.M.A.R.T. status
Disk Utility shows a drive’s S.M.A.R.T. status.
Most modern hard drives have built-in sensors and monitoring circuitry that form a system called S.M.A.R.T. (Self-Monitoring Analysis and Reporting Technology). The idea of S.M.A.R.T. is to detect the warning signs of potential problems
they occur. Although S.M.A.R.T. cannot detect every possible drive problem, it can provide one very valuable warning: “Your drive is about to have problems, so back it up and repair (or replace) it now!”
: As of early 2006, Disk Utility’s S.M.A.R.T. indicator works with internal ATA and Serial ATA drives, but not with external (USB or FireWire) drives. Some external drives, however, have their own built-in S.M.A.R.T. indicators.
To check your drives’ S.M.A.R.T. status, open Disk Utility (in /Applications/Utilities) and select a drive in the list on the left. If the selected drive supports S.M.A.R.T., you should see this at the bottom of the window: “S.M.A.R.T. Status: Verified.” If you see “About to Fail” in red letters, back up the drive immediately. You can then use Disk Utility (or a third-party repair utility) to attempt to repair the drive, but more often than not, “About to Fail” indicates an imminent hardware failure that you cannot fix with software. Even if Disk Utility does appear to solve the problem, don’t trust the drive with important data; replace it as soon as possible.
: To monitor your drives’ S.M.A.R.T. status in the background (without having to remember to open Disk Utility), try the free utility
SMARTReporter, which displays a status icon in your menu bar.
Joe Kissell is a frequent contributor to
and has written numerous books and ebooks about the Macintosh; his latest is
Take Control of Maintaining Your Mac
(TidBits Electronic Publishing, 2006).