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Technical Note #1
Subject: Macintosh Extensions and Problems They Cause
Created: November 2, 1997
Last Updated: December 3, 2002
Important note about Mac OSX.
Extensions, as they are described in this techincal note, can exist only in Mac OS 9 and earlier. OSX (Mac System 10) does not utilize or allow extensions, therefore this technical note does not apply to OSX. However, extensions can still exist within the "Classic" OS 9 environment supported under OSX. Extensions running inside the Classic environment can affect Classic based applications, but have no effect on native OSX applications or the OSX environment.
What is an extension?
Many people think of an extension is any file that is put inside the Extensions folder (which is located inside the Macintosh System Folder). Note that the term "extension" may be used to describe different things, but this technical note is concerned only with the kind of extension that modifies the Macintosh behavior. These type of extensions are also called INITs, because they become active when your Macintosh starts up (during the INITialization of the system). Because INIT extensions change the behavior of the basic System, they are one of the most common cause of instability and problems on a Macintosh. Throughout the rest of this report the term "extension" refers specifically to INIT extensions.
What is the purpose of an extension?
Extensions are a way to add functionality to the Macintosh System Software that does not currently exist. INIT extensions usually modify the System Software as the computer is starting up. The System stays in this modified state as long as it is running. To stop an extension from running, you must disable it and then restart the computer (disabling is discussed later).
An extension can produce new behavior or add new features not available in standard System Software. Some applications, such as fax software, use extensions to add functionality to the System for their benefit only. Other extensions, such as a screen saver, might change the way the entire Macintosh looks or behaves no matter what application might be running at the time.
Because INIT extensions modify (or "patch") the System Software, they must be careful not to interfere with the normal operation of the Macintosh as Apple has designed it. It is possible that multiple extensions might attempt to modify the same part of the System, which can sometimes produce unexpected results. You will find that these modifications of the System will eventually cause problems as you add more extensions or if Apple changes the way the System works.
Where do extensions come from?
Some extensions are created by Apple Computer, and are included with System Software. QuickTime, for example, is an Apple extension that adds more graphics and video capabilities to the Macintosh. Extensions are included with many of the applications that you buy. When you install an application that includes extensions, the extensions are usually automatically installed when you install the application. Sometimes extensions that are included with applications are optional and not required to run the software. In these cases, you can remove some extensions if you do not feel you need the features they provide. Fax software almost always comes with several extensions that are required.
How do I know if my Macintosh has extensions?
If you have extensions, you will see icons (small pictures) appear starting in the lower left part of the screen when you start up the Macintosh. However, be aware that some extensions may not display an icon when they load themselves into the System. Fortunately, most extensions will show an icon. If you are running System Software 7.5 or higher, you can see extensions with the help of a control panel called Extensions Manager (which is explained later in this document).
What kind of problems can extensions cause?
Extensions are one of the largest causes of problems and instability on your Macintosh.
When Apple releases upgrades to System Software or new models of computers, many extensions will no longer work properly and will often cause strange behavior, such as applications unexpectedly quitting and the entire computer freezing up. In these causes, you must contact the creator of the problem extension to see if they have a new version that corrects the problem.
Some extensions can use up a lot of your available memory (RAM). To see how much memory the extensions are using, choose "About this Macintosh" from the Apple menu, and notice how much memory is being used by System Software. Then start the Macintosh while holding the Shift key down (this temporarily disables all extensions). Again, choose "About this Macintosh" from the Apple menu and notice the difference in the amount of memory in use by System Software. This difference is the amount of memory being used by the extensions.
How can I solve extension problems?
There are two ways to solve an extension problem. The first is to call the developer of the extension to make sure it is compatible with the version of the Macintosh System Software you are using. If it is not compatbile, get the most recent version that is compatible. The second way is to discontinue using the extension by removing it or disabling it (this is covered later on).
Where are extensions kept on my Macintosh?
Extensions are stored in one of three places: 1) System Folder; 2) Extensions folder; 3) Control Panels folder. The second two folders (Extensions and Control Panels) are folders that are inside the System Folder. You may think that all extensions should go in the Extensions folder, but they can actually reside in any of the three locations mentioned. If an extension is not located in one of required folders, it will not be seen by the System and will not be effective. Note that in System 6, all extensions were stored in the System Folder.
How do I know which files are extensions?
Determining which of the files in the Extensions folder, Control Panels folder, or System Folder are INIT-based extensions can be difficult. If you are using System Software 7.5 or higher, you can use the Extensions Manager, which is a control panel that shows you what extensions you have and lets you selctively disable them. See the topic "How can I disable extensions" below for more information on the Extensions Manager.
If you do not use the Extensions Manager, you must start up the Macintosh and make a mental note of the icons that appear starting in the lower left part of the screen. After the Macintosh is done starting up, search the Extensions folder, Control Panels folder, and the System Folder for files that have the same icons as the ones you saw when starting up. When viewing a folder, you may need to choose "by Icon" from the "View" menu if the folder is not already being displayed with icons. Be aware that some extensions may not display an icon when they load themselves into the System. Fortunately, most extensions will show an icon.
How can I disable extensions?
There are three ways to disable an extension.
The first method works with System Software 7.0 or higher. Simple start or restart the Macintosh while holding the Shift key down. Continue holding the Shift key down until you see a message indicating "Extensions Off", then you may release the key. The Macintosh will start up without loading any of the extensions, even if they are in their proper location. This is a temporary way to disable extensions, because to keep the extensions disabled, you must hold down the Shift key every time you start or restart the computer.
The second method to disable an extension is to move it to location where it will not be seen and then restart the Macintosh. You can move it to anywhere other than the Extensions folder, Control Panels folder, or the System Folder. Since extensions are loaded when your Macintosh starts up, moving the extension without restarting does nothing, becuase the extension has already been loaded during the last startup. When you restart, the Macintosh will ignore the extension you have moved.
The third method for disabling extesions is available with System Software 7.5 or higher. The Extensions Manager control panel allows to to selectively disable and enable extensions. It shows you all of the extension files currently existing in your Extensions folder, Control Panels folder, or System Folder. When you disable an extension, the Extensions Manager moves the extension to a special folder where the System will not see it when you restart the Macintosh. This method of disabling is the same as the second method mentioned above, except that the Extensions Manager makes it much easier. You can even have it remember certain combinations of extensions to load. If you have System 7.5 or higher it is highly recommended that you use the Extensions Manager instead of moving files manually.
If you are using System 6, the second method mentioned above is the only way to disable an extension.
Which extensions should I use?
Generally, extensions created by Apple Computer are the most reliable. This is because when Apple makes a change in the System Software, they make any changes that are necessary to any existing extensions. They usually include the updated extensions when you update to a newer version of the System Software. For extensions not created by Apple, you must make sure that they are compatible with the new System Software.
How can I determine which extensions are causing problems?
This can be a very lengthy task. You first disable all extensions and then restart the Macintosh to see if that eliminates the problem. If that solves the problem, you enable each extension, one at a time, and restart the Macintosh to test for the problem. Once the problem appears, you know that the last extension you enabled was the source of the problem. You then can obtain an upgrade to a newer version of the extension that fixes the problem, or discontinue use of that extension.
Sometimes a problem is caused by a combination of two ormore extensions. Each extension might work fine by itself, but when used with one or more other extensions, it can cause a problem. Unfortunately, this type of problem is one of the most difficult to diagnose.
Be aware that if you are having a problem with an application, you may not even be able to start the application if you disable an extension that the application requires. Hopefully, the application will work sufficiently without its extension so that you see if the problem is resolved.
All else fails, you could consider purchasing software now available that helps you find conflicts and incompatibilites with extensions.
What can I do to reduce the problems I have with extensions?
The best advice to reduce problems and keep a stable Macintosh is to use as few extensions as possible. When you purchase new software that loads new extensions onto your Macintosh, try to determine if the extension is required or optional. If optional, decide whether you need its functionally, then consider removing or disabling it. The author of this report has been using Macintosh for over 10 years, and has noticed his Macs are more stable than most other users. It is probably because those Macs are always kept "clean" with a very minimum number of necessary extensions.
What extension problems should I expect in the future?
Future versions of the Macintosh System Software most likely will have new requirements for extensions. It is possible with future systems, that none of the INIT extensions available today will work unless they are redesigned by their developer. When you are considering upgrading to a newer Mac System, remember that many of your extensions may no longer work.
Summary
INIT extensions are one of the most common cause of instability and problems on a Macintosh. Extensions are included with many of the applications that you buy. If you have extensions, you will usually see icons (small pictures) appear starting in the lower left part of the screen when you start up the Macintosh. When Apple releases upgrades to System Software or new models of computers, many extensions will no longer work properly and will often cause strange behavior.
If you have an extension problem, you call the developer of the extension to make sure it is compatible with the version of the Macintosh System Software you are using. You could also discontinue using the extension by removing it or disabling it. A future versions of the Macintosh System Software may not be able to use existing INIT extensions. The best advice to reduce problems for now is to keep a stable Macintosh by relying on as few extensions as possible.