Multifinder

MultiFinder was the name of an extension software for the Apple Macintosh's classic Mac OS, introduced on August 11, 1987 and included with System Software 5. 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 and remained until the introduction of Mac OS X.

The first Macintosh, released in 1984, had such limited memory (128 kB) 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 and to make good on the GUI's promise of interface consistency, the original Macintosh included Desk Accessories, such as a calculator, that could be run concurrently. However, these were deliberately limited so that they would not use up too much of the available RAM. In fact, they were device drivers which took advantage of the multitasking system designed for hardware peripheral support. As such, their running environment was severely restricted. They could only draw a single window (which by default was given a special round-bordered appearance) and could only run during the vertical blanking interval, which meant that they had to complete processing and redraw themselves every 1/60th second. Since they also couldn't spawn new processes, this made long-running background tasks impossible. Although the system software did little to specifically support them, the popularity of Desk Accessories led many application developers to ensure good cooperative multitasking support even from the early days.

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