About Control Panels
In System 7.0 and above, the Control Panel desk accessory no longer exists as one entity. Each of the individual control panels now appears as a modeless
dialog box. Users can open control panels in the same way as any other
document, and several control panels can be open at one time. The main reason
to create a control panel file rather than an application is to maintain
compatibility with the Control Panel for users who are using earlier operating systems. Any control panel file that follows the rules and suggestions
given in the Control Panel chapter of Volume V will continue to work without problems in System 7.0 (or above).
A control panel can open in a window of any size. However, you may want to
constrain any new panels that you develop to fit in the space provided by the
previous Control Panel desk accessory. Doing so guarantees that the control panel can be opened either by the Control Panel desk accessory in earlier versions of system software or by the Finder in System 7.0.
The user can store control panels in the Control Panels folder or the Apple
Menu Items folder (both in the System Folder), or at any other location in the
file system.
You should refer to a file of type 'cdev' as a control panel file in any user
documentation that you provide. Don't pass on the file type name of this file or
any other file to users.
control panels that work in all versions of system software.