MultiFinder

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MultiFinder was the name of a piece of extension software for the Apple Macintosh, introduced in System Software 5 in 1988 and included with System Software 6. It added the ability to co-operatively multitask between several applications at once – a great improvement over the previous systems, which could only run one application at a time. With the advent of System 7, MultiFinder became a standard integrated part of the operating system.

MultiFinder was an obvious response to the needs of users, but it had an interesting history. The first Macintosh had such limited memory that Apple's developers decided early on to abandon the multi-tasking that Apple had developed for the Lisa. To allow some degree of freedom, the Mac added Desk Accessories, but these were deliberately limited so that they would not use up too much of the RAM available. Each new Macintosh model included more RAM than the previous models, with 1MB becoming standard on the Mac Plus. This amount of RAM was sufficient to support some form of multitasking, which was first implemented by Andy Hertzfeld in his Switcher program. Switcher worked by designating a number of fixed "slots" in memory, into which applications could be loaded. The user could then switch between these applications by clicking a small button on the top of the menu bar. The current application would horizontally slide out of view, and the next one would slide in. Despite its awkwardness, this approach did fit well with the existing system's memory management scheme, and applications needed no special programming to work with Switcher. The early work on Switcher led to the development of MultiFinder by Apple system software engineers Erich Ringewald and Phil Goldman.

MultiFinder extended the system in a number of significant ways. In addition to giving each application CPU time, it provided a way for windows from different applications to co-exist by using an application layering model. When an application was activated, all of its windows were brought forward as a single layer. This approach was necessary for backward compatibility with many of the windowing data structures that were already documented. It also provided a way for applications to supply their memory requirements ahead of time, so that MultiFinder could allocate a chunk of RAM to each according to need. This scheme, while functional, turned out to have severe limitations which caused many problems for users (see Mac OS memory management for more details). The integration of MultiFinder into System 7 did nothing to fix these shortcomings.

While MultiFinder as a separate entity disappeared after System 6, its legacy remained in the System all the way up to Mac OS 9. Only with the move to a modern preemptive multitasking UNIX-based OS in Mac OS X were the idiosyncrasies and disadvantages of MultiFinder finally overcome.it:MultiFinder