Extension conflict
Encyclopedia
Extension conflicts were sometimes a problem on Apple Macintosh computers running versions of Mac OS
prior to X
, especially System 7
. Extension
s were bundles of code that extended the operating system
's capabilities by directly patching OS calls
, thus receiving control instead of the operating system when applications (including the Finder
) made system calls. Generally, once an extension had done what it wanted, it was supposed to pass on the (possibly modified) system call to the operating system's routine. If multiple extensions want to patch the same system call, they end up receiving the call in a chain, the first extension in line passing it on to the next, and so on, until the last extension passes to the operating system. If an extension does not hand the next extension in line what it is expecting, bad things result, ranging from unexpected behavior to full system crashes.
In addition, extensions sometimes competed for system resources with applications
, utilities and other extensions, leading to crashes
and general instability. Many users happily loaded every extension they could find on their computer, with little or no impact. Others fastidiously avoided any non-essential extensions as a way of avoiding the problem. Others were judicious in the addition of extensions.
This problem increased during the mid-1990s as resource-hungry multimedia
technologies such as QuickTime
were installed as extensions. In addition, a number of applications, especially Microsoft Office
, required a large number of extensions. Many Macintosh users had hundreds of extensions running on their systems, all of varying age and quality. Buggy, damaged and outdated extensions were the most common cause of problems. Some users had to remember to turn off problematic extensions when running certain programs.
Later versions of System 7 included the Extensions Manager, which allowed users to turn off specific extensions or groups of extensions at startup. Conflict Catcher
, a third party utility, automatically detected conflicts and problematic extensions, otherwise a time-consuming task that required users to turn off extensions in sets until they found the conflict. Extensions were only loaded at startup time, meaning that any attempted change required a reboot.
The most common time for extension conflicts to start was the release of a new version of the operating system, followed closely by the installation of a new application that either conflicted with existing extensions, or installed extensions that conflicted with the existing set.
All of this was mitigated by the ease with which extensions and the operating system itself could be swapped in and out: Instead of modifying configuration files as on other operating systems, extensions simply had to reside in a particular folder to be picked up. In addition, the Mac was perfectly happy to have two (or more) system folders present on a hard drive. Only the "blessed" system folder would be loaded at startup. So, when a new version of the operating system was to be installed, or a new application, the user could easily duplicate the system folder, perform the install, and then fall back if a problem resulted.
Extension conflicts came to an end with the release of Mac OS X, which uses a different extension mechanism.
Mac OS
Mac OS is a series of graphical user interface-based operating systems developed by Apple Inc. for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface...
prior to X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
, especially System 7
System 7 (Macintosh)
System 7 is a single-user graphical user interface-based operating system for Macintosh computers. It was introduced on May 13, 1991 by Apple Computer. It succeeded System 6, and was the main Macintosh operating system until it was succeeded by Mac OS 8 in 1997...
. Extension
Extension (Mac OS)
On the Apple Macintosh operating system prior to Mac OS X, extensions were small pieces of code that extended the system's functionality. They were run initially at start-up time, and operated by a variety of mechanisms, including trap patching and other code modifying techniques. Initially an...
s were bundles of code that extended the operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
's capabilities by directly patching OS calls
System call
In computing, a system call is how a program requests a service from an operating system's kernel. This may include hardware related services , creating and executing new processes, and communicating with integral kernel services...
, thus receiving control instead of the operating system when applications (including the Finder
Macintosh Finder
The Finder is the default file manager used on Mac OS and Mac OS X operating systems; it is responsible for the overall user-management of files, disks, network volumes and the launching of other applications...
) made system calls. Generally, once an extension had done what it wanted, it was supposed to pass on the (possibly modified) system call to the operating system's routine. If multiple extensions want to patch the same system call, they end up receiving the call in a chain, the first extension in line passing it on to the next, and so on, until the last extension passes to the operating system. If an extension does not hand the next extension in line what it is expecting, bad things result, ranging from unexpected behavior to full system crashes.
In addition, extensions sometimes competed for system resources with applications
Application software
Application software, also known as an application or an "app", is computer software designed to help the user to perform specific tasks. Examples include enterprise software, accounting software, office suites, graphics software and media players. Many application programs deal principally with...
, utilities and other extensions, leading to crashes
Crash (computing)
A crash in computing is a condition where a computer or a program, either an application or part of the operating system, ceases to function properly, often exiting after encountering errors. Often the offending program may appear to freeze or hang until a crash reporting service documents...
and general instability. Many users happily loaded every extension they could find on their computer, with little or no impact. Others fastidiously avoided any non-essential extensions as a way of avoiding the problem. Others were judicious in the addition of extensions.
This problem increased during the mid-1990s as resource-hungry multimedia
Multimedia
Multimedia is media and content that uses a combination of different content forms. The term can be used as a noun or as an adjective describing a medium as having multiple content forms. The term is used in contrast to media which use only rudimentary computer display such as text-only, or...
technologies such as QuickTime
QuickTime
QuickTime is an extensible proprietary multimedia framework developed by Apple Inc., capable of handling various formats of digital video, picture, sound, panoramic images, and interactivity. The classic version of QuickTime is available for Windows XP and later, as well as Mac OS X Leopard and...
were installed as extensions. In addition, a number of applications, especially Microsoft Office
Microsoft Office
Microsoft Office is a non-free commercial office suite of inter-related desktop applications, servers and services for the Microsoft Windows and Mac OS X operating systems, introduced by Microsoft in August 1, 1989. Initially a marketing term for a bundled set of applications, the first version of...
, required a large number of extensions. Many Macintosh users had hundreds of extensions running on their systems, all of varying age and quality. Buggy, damaged and outdated extensions were the most common cause of problems. Some users had to remember to turn off problematic extensions when running certain programs.
Later versions of System 7 included the Extensions Manager, which allowed users to turn off specific extensions or groups of extensions at startup. Conflict Catcher
Conflict Catcher
Conflict Catcher was a popular utility software application for the Mac OS, written by Jeff Robbin and published by Casady & Greene. It aided Macintosh users in solving operating system conflicts with extensions and control panels...
, a third party utility, automatically detected conflicts and problematic extensions, otherwise a time-consuming task that required users to turn off extensions in sets until they found the conflict. Extensions were only loaded at startup time, meaning that any attempted change required a reboot.
The most common time for extension conflicts to start was the release of a new version of the operating system, followed closely by the installation of a new application that either conflicted with existing extensions, or installed extensions that conflicted with the existing set.
All of this was mitigated by the ease with which extensions and the operating system itself could be swapped in and out: Instead of modifying configuration files as on other operating systems, extensions simply had to reside in a particular folder to be picked up. In addition, the Mac was perfectly happy to have two (or more) system folders present on a hard drive. Only the "blessed" system folder would be loaded at startup. So, when a new version of the operating system was to be installed, or a new application, the user could easily duplicate the system folder, perform the install, and then fall back if a problem resulted.
Extension conflicts came to an end with the release of Mac OS X, which uses a different extension mechanism.
See also
- Configuration managementConfiguration managementConfiguration management is a field of management that focuses on establishing and maintaining consistency of a system or product's performance and its functional and physical attributes with its requirements, design, and operational information throughout its life.For information assurance, CM...
- Dependency management
- DLL hellDLL hellIn computing, DLL Hell is a term for the complications that arise when working with dynamic link libraries used with Microsoft Windows operating systems, particularly legacy 16-bit editions which all run in a single memory space....