123. Set the Computer's Sleep Time  BEFORE YOU BEGIN 25 Set the Time and Date 26 Enable Automatic Time Synchronization (NTP)
 SEE ALSO 115 Require a Password When Reactivating the Computer 114 Automatically Log Out
123. Set the Computer's Sleep Time 
One of the first and simplest energy-saving things you can do with your Mac is to configure it to put itself to sleep after a certain period of inactivity. If you don't touch your keyboard or mouse for that length of time, the computer will automatically go to sleep; you can then wake it up by pressing a key or moving the mouse.  NOTE There are a few conditions under which your computer won't go to sleep, even if you haven't touched your keyboard or mouse. If a QuickTime movie or a DVD is playing, for instance, Mac OS X will recognize that something's going on and will not dim the screen or put the computer to sleep.
You can also configure separate sleeping behaviors for your display and your hard disk; you might want your screen to turn off after an hour of inactivity, for instance, or your hard drive to spin down, and yet for your computer to not fully go to sleep until another hour has passed. These things are all configurable in the Energy Saver Preferences pane. | 1. | Open the Energy Saver Preferences Open the System Preferences application (under the Apple menu); click Energy Saver to bring up the Energy Saver Preferences pane. Click the Sleep tab if it's not already selected. If you have a desktop Mac (an iMac, eMac, or Power Mac), the Energy Saver Preferences pane will simply show the three tabs for configuring power management behavior: Sleep, Schedule , and Options . However, if you have a laptop (an iBook or PowerBook), the Energy Saver Preferences pane has an Optimize Energy Settings drop-down menu that lets you select from several predefined energy-saving profiles (optimized for various styles of computer usage) or create your own profile, and a second Settings for drop-down menu that lets you configure the settings separately for whether your computer is plugged in or using battery power. You can also show or hide the details of the window, using the Show Details or Hide Details button in the lower-right corner; when the details are hidden, the only controls that are visible are the ones that let you select an energy profile for your different power sources. NOTE The illustrations for this task show the Energy Saver Preferences pane for a laptop (a PowerBook, to be precise). On non-laptop Macs, the Show/Hide Details button is instead a Restore Defaults button. | | 2. | Set the Sleep Time Use the Put the computer to sleep when it is inactive for slider to select a sleep time. Mac OS X has different default configurations depending on whether it is running on a laptop or a desktop Mac, or whether the power source is the battery or the AC adapter. On continuous power, it never automatically sleeps, so the slider is in the Never position at the far right; on battery power, it is set to sleep after 10 minutes of inactivity. You can disable automatic sleep by moving the slider all the way to the right. NOTE Notice that the slider's numbering is not linear. At the far left, individual minutes are far apart, so that you can easily select between four and five minutes; but as you move the slider to the right, the numbers increase faster so that you can select up to three hours of inactivity. | | 3. | Set the Display Sleep Time Normally, your whole computer will go to sleep at once, after the inactivity period you specify has elapsed. However, you can choose to set your Mac to put only its display to sleep, but to keep the computer itself running. This can be useful if you like to keep certain programs running all night long while you sleep, but you don't want to waste energy keeping the screen lit if nobody's looking at it. Your display will dim (to about half its normal brightness) when the computer has been inactive for half the time it takes to go to sleep or (if you have enabled a separate display sleep time) for the display to sleep. This is useful primarily for laptops, in which the screen is one of the biggest consumers of power; dimming the screen helps reduce power usage. (You can disable dimming using the Automatically reduce the brightness of the display before display sleep check box under the Options tab.) Select the Put display to sleep when the computer is inactive for check box to enable a separate display sleep time, and set the inactivity period by sliding the pointer to a point to the left of the first slider's pointer. You can reset the display's sleep time to match the system sleep time by moving the second slider to the right until it is in sync with the computer sleep slider. Similarly, if you move the computer sleep slider farther left than your display slider is set, both sliders will move in unison to keep their values synchronized. NOTE If you have a screensaver enabled, Mac OS X warns you if you try to set the system to sleep earlier than how long it takes for the screensaver to kick in. If you set the system to sleep automatically after a certain period of inactivity, visit the Desktop & Screen Saver Preferences pane to ensure that the screensaver will activate at an appropriate time. See 104 Select a Screensaver . | | 4. | Allow the Hard Disks to Sleep
Use the Put the hard disk(s) to sleep when possible check box to specify whether or not you want the hard disk to spin down whenever the system determines it's not being used (usually after a few minutes of inactivity). If you allow the hard disk to sleep, its lifetime will be increased; however, it will take several extra seconds for the system to become responsive , as it spins the disk back up again, if you suddenly need to access the disk after it's been shut down.
| | 5. | Adjust Processor Performance
Click the Options tab. Use the Processor Performance drop-down menu to select how fast you want your computer's processor to run. With the processor set to Highest performance, the computer will run at full speed, but power consumption will be higher than if you select Reduced , which causes the processor to run at a slightly slower speed. Generally this is meaningful only for laptops, but some computers with complex cooling systems (such as the Power Mac G5) also behave differently according to how this option is set.
| | 6. | Require a Password When Waking from Sleep
If you have a laptop, especially one with sensitive information on it, it's a good idea to configure Mac OS X to require your password when the Mac wakes from sleep. To do this, open the Security Preferences pane (click Security in the System Preferences application). Use the Require password to wake this computer from sleep or screen saver check box to make it so that a thief who makes off with your laptop won't be able to access your sensitive documents. (See 136 Secure Your Files with FileVault for an additional precaution you can take if your laptop's data is really sensitive: encrypting your entire Home folder.)
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