And then there’s the Screen Saver tab. Before I delve into its mysteries, a little background.
In the days when Macs weren’t as thin as the worst sort of fashion model, users viewed the Mac interface through CRT (cathode ray tube) monitors—akin to the large picture-tube-bearing televisions of the time. These monitors were prone to a condition called screen burn-in: The phosphor inside the CRT could permanently take on an image when that image was projected to it for months on end—the image of the Mac’s menu bar, for example, was commonly burned in. The burn-in left ghost images on the display that were distracting.
To help prevent burn-in, companies created screensavers—applications that would automatically kick in after a period of computer inactivity and display moving images rather than static ones. After Dark’s Flying Toasters was the most well-known of these products.
Since today’s monitors don’t suffer from this kind of burn-in, screensavers often serve as an amusement rather than as a prophylactic measure (though they have a practical use that I’ll address shortly).
When you click the Screen Saver tab, you’ll see that Mountain Lion’s screensavers are broadly arranged in two categories: slideshows and screensavers. In the Slideshows area, you'll find 14 slideshow effects. These can show images from a variety of sources, including your iPhoto and Aperture libraries, images from National Geographic, images supplied by Apple, and a folder or photo library of your choosing. You pick the source from the aptly named Source pop-up menu.
Below the slideshow area are Mountain Lion’s screensavers. These include three computer-generated patterns, a message of your choosing, album covers from your iTunes library, and a "Word of the Day" that travels across your screen along with its definition. Choose Random, and the screensaver will be one of the six alternatives chosen at the OS’s whim. Some of the screensavers have options that you can explore by clicking the Screen Saver area's Options button.
To test the look of a slideshow or screensaver, select it on the left side of the window, hover your pointer over its image on the right side of the window, and click the Preview button that appears. The slideshow or screen saver will expand to full screen. To stop it, just click anywhere.
At the bottom of the window, you’ll see a few additional options. The first is 'Start after'. This is where you choose the period of inactivity (meaning you haven’t touched the mouse, trackpad, or keyboard) after which the slideshow or screensaver begins. You have choices from 1 minute to 1 hour. The next option, 'Show with clock', displays a clock over the screensaver when enabled.
About Hot Corners
The last option, Hot Corners, deserves a bit more explanation. When you click this button, a sheet will appear that shows four pop-up menus corresponding to the four corners of your Mac’s display. Click one of these menus, and you see several commands: Start Screen Saver, Disable Screen Saver, Mission Control, Application Windows, Desktop, Dashboard, Notification Center, Launchpad, Put Display to Sleep, and a dash, which indicates "Don’t Do Anything, Thank You Very Much."
You assign these commands to the various corners of your display. For example, you might assign Start Screen Saver to the top-left corner. Do that and click OK; when you drag your pointer to this location on the screen, the screensaver kicks in. Move your pointer, and the screensaver disappears. In short, it’s a quick way to invoke one of these commands.
Before committing to a hot corner, examine how you use your Mac. If you often drag your pointer to the bottom-left corner to access the Dock, assigning a command to that hot corner probably isn’t such a hot idea, as your Mac will do something that you didn’t intend. Rather, place that command in a corner that you’d touch for only that specific purpose.
Screensavers and security
Earlier I mentioned that screensavers serve little useful purpose, and I promised to show a hidden talent. You’ll find that talent in the Security & Privacy system preference. Select that preference and then click the General tab if it’s not already selected. Click the lock icon at the bottom of the window and enter your username and password. The option you’re looking for is 'Require password [some amount of time] after sleep or screen saver begins'. Configure its pop-up menu to read immediately. Now, when your Mac goes to sleep, you invoke the screensaver, or the screensaver starts on its own, and you’ll be required to enter your account password before you can use your Mac.
This is a particularly useful option to enable if your Mac is in a location where other people can access it—your office, say, or within reach of a surly teenager. Just shove your pointer into the appropriate hot corner, and you can step away without fear that someone without your password can muck with your Mac.
Next week: About Mission Control