Apple Computer Inc has filled in a little more of its forthcoming operating system software strategies in a new Mac OS white paper. As expected the ‘Copland release’ of the operating system will be microkernel-based and will introduce the first pre-emptive multi-tasking. It will also see substantial amounts of the operating system move from running under emulation to running as native PowerPC code. There is, in addition, the promise of a high performance 68000 emulator. While Apple is saying little else, MacWeek reporter Robert Hess has been talking to what sound like authoritative sources and has come up with details of how Apple intends to avoid breaking today’s applications that use programming techniques incompatible with the protected memory systems needed for pre-emption. According to MacWeek, Copland will load the Mac Toolbox into its own separate protected memory segment to avoid applications from treading on it. All old-style Macintosh applications and extensions will share another single address space, dubbed the ‘Blue Box’ by the paper. Copland-aware applications, however, will be allocated their very own protected memory segments. The practical upshot is that, if an old-style Mac program crashes, it may bring down all of the other applications running in the Blue Box, just as they can in today’s Macs. The separate, pre-emptive applications should be isolated from such mishaps, however. Copland applications will be able to spawn separate tasks, or threads, each within their own address space, but the MacWeek article suggests that these threads will be granted only limited access to Toolbox routines, so they will not be able to write to the screen directly, though they will probably be able to use input-output. However, it seems likely, therefore, that even Copland-designed applications will tend to be hybrids, with Toolbox-intensive parts sitting in the Blue Box, with the rest outside – which means that they will not be fully protected after all. While Copland is a half-way-house to full pre-emption, its successor, code-named Gershwin is being touted as the real thing. The company’s white paper promises advanced multi-tasking and memory protection for all processes, sub-processes and applications. It is also promised to be based on the OpenDOC component software from top to bottom. However, it is clear that these promises can only come true if developers follow Apple’s lead.
