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In 1985 a previously unknown individual by the name of Jwa van der Vuurst released Multi-Mac, which made true multitasking possible on a Macintosh 512K, using the 64K ROM, Finder 4.1 and System 2.0. Subsequent versions of Macintosh System Software through version 6 would work with Multi-Mac, but only on a Macintosh with the original 64K ROM.






While the application quickly made the rounds on bulletin boards, Apple claimed to know nothing about the software. The copyright, by Aubrac Systems, prevented big boards like CompuServe and Genie from distributing the application. The program supposedly makes over 200 direct calls to undocumented addresses in the ROM, while allowing users to configure memory allocations, have multiple applications loaded in the Macintosh's memory at the same time, and directly control the disk cache. For many Macintosh users with brand new Fat Macs equipped with 512K of RAM, this System enhancement made the efficiency promised by computers possible. Dave Morris, in his contemporary review of Multi-Mac, wrote, "It was possible for instance to be downloading a long file via a telecom program, and writing a letter in MacWrite at the same time you were printing out a spreadsheet." Multitasking was possible on the Macintosh without the additional hardware Apple claimed was necessary. The sheer brilliance of its capabilities and the complex ROM calls made by this application led many to believe that Andy Hertzfeld was behind this enhancement to the Macintosh experience.


Multi-Mac supplements Finder 4.1 on the 64K ROM Macs, namely the Macintosh 512K. When launched, Multi-Mac integrates itself into the Finder, System, and the ROMs. Change to the GUI is minimal: there is an Apple menu in the upper right corner of the Menu bar, under which one has access to programs that are running. The Multi-Mac Options, shown above, are also available from this Application menu. Users are able to allocate how much memory is used for a particular application, as well as its priority in CPU usage. By checking Save Whole Screen the contents of the screen are saved in memory, making switching between applications seem faster as screen redraws are minimized, at the expense of using more memory. By clicking Install one can select which applications one wants to run. Select which program should be in the foreground, click Run and this application will begin running. Programs can be switched from the Multi-Mac menu in the Menu bar. Remove will force quit an application, but not as gracefully as Quitting from the application itself; this is a remedy for a hanging application. Lazy Menu will open menus without the user clicking on them; simply directing the mouse towards the menu will cause it to open. Finally, the disk cache exists, and can be controlled, before the new 128K ROMs introduced with the Macintosh Plus existed.

Within the confines of the old ROM used by the Macintosh 512K, Multi-Mac worked well. It allowed for real multitasking, as multiple processes could take turns using the CPU, instead of one process or application taking up all of the CPU cycles. However, it was obsolete, and would not run, on the next generation Macintosh Plus, which contained the 128K ROMs. A different program would be needed to allow Macintosh users to run mulitple programs at the same time.



copyright 2002 Josh Burker



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