We have several Power Macintosh computers in our office and we have a mixture of Apple displays computers running different versions of the Mac OS.

When we go into the Monitors & Sound control panel on our different computers, we notice that we each get different display resolution options.

1. How does the Monitors & Sound control panel know which display resolutions are available?
2. How can we tell which display resolutions should appear as options in the Monitors & Sound control panel?
3. What is the difference between "Recommended" and "All" display resolutions in the Monitors & Sound control panel?
4. Why does Apple include both Macintosh and VGA or VESA resolutions on Power Macintosh computers?

Answer: The Monitors & Sound control panel depends on a component of the Mac OS called the Display Manager. The Display Manager allows you to dynamically change the arrangement and display modes of the displays attached to the computer.

The video device driver is also responsible for telling the Display Manager what display modes are available. In determining what type of display is attached to your video port, device drivers usually examine the display's sense code. A device driver can associate each sense code with a default display mode and a set of required and optional display modes for the display.

The latest version of the Apple Displays software at the time of this writing is version 1.7.1. This software is available from the Apple Software Updates Web site at http://www.apple.com/swupdates . For more detailed information regarding the Display Manager and video device drivers, refer to the Display Device Driver Guide and Display Manager documentation available on Apple's Developer Web site at http://www.apple.com/developer .

Question: How can we tell which display resolutions should appear as options in the Monitors & Sound control panel?

Answer: Most Power Macintosh computers ship with a Technical Information booklet that details the video modes supported by that particular computer. In some cases, this information is provided as a section in the User's Manual/Guide. This information should tell you what resolution and screen refresh rates your computer is capable of. With this information, you can check with your display's documentation to see what resolutions and refresh rates it supports.

As long as the computer and display's supported resolutions and refresh rates match, these resolutions and refresh rates should appear in the Monitors & Sound control panel under "Recommended" or "All" display resolutions. If these resolutions do not, you may not have the correct display software installed on your computer or the display may not be properly connected to the computer.

Question: What is the difference between "Recommended" and "All" display resolutions in the Monitors & Sound control panel?

Answer: In most cases, you will want to select from the Recommended choice of resolutions. These resolutions are known to work well with the monitor attached to your computer. Also, these are also the required and default display modes for your computer. All required display modes appear when the user opens the Monitors and Sound control panel. For a particular type of display (for example, a 21-inch video monitor), a required display mode is one that Apple requires the display to support.

On some Macintosh and Power Macintosh computers, users can choose All resolutions from the Monitors & Sound control panel to reveal additional resolutions that your monitor might also support. This might be useful if your computer provides video output or video mirroring to a TV or VCR. Some resolutions that appear under "All" may look better than those that are recommended. Some of these resolutions that appear under "All" might cause the picture to flicker or be distorted. If you choose a resolution from the list, and your monitor goes black, wait a few seconds and it will return to its previous setting.

Question: Why does Apple include both Macintosh and VGA (Video Graphics Array)/VESA (Video Electronics Standards Association) resolutions on Power Macintosh computers?

Answer: Most of the recent Power Macintosh computers are compatible with Windows-based VGA/VESA displays in addition to Apple displays. If our Power Macintosh computers only supported Macintosh resolutions, customers would have less of a choice in the displays they use.

Additionally, most of the recent Apple Displays are cross-platform displays that can be used on both Macintosh and PC computers. This is why you will see both Macintosh and VGA/VESA resolutions appearing on some Power Macintosh computers when an Apple Display is connected.