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68k system on PowerPC?
Posted: May 7th, 2009, 4:54 am
I recently installed a hard drive from a 68k machine with OS 7.6 in a PPC 6100. I was amazed that it booted. I thought the code set for PPC was different from 68k???? Shouldnt this not work???? RAy.
Re: 68k system on PowerPC?
Posted: May 7th, 2009, 8:39 am
A default installation "for all Macintoshes" of Mac OS 7.6 will includes both 68k and PowerPC code where PowerPC code is available. They're called Fat Binaries
. Apple reintroduced the concept for the Intel switch, calling them Universal Binaries. Any 68k-only code runs in emulation on a PowerPC.
A fat binary program (often simply called a fat program) is an program that contains executable code for more than one runtime architecture. Typically you create fat programs when you want compatibility between hardware platforms. For example, a fat application with PowerPC code and CFM-68K code can be executed on both PowerPC-based and 68K-based Macintosh computers. A user can store a fat application on a portable hard drive and then move it between a 68K-based computer and a PowerPC- based computer.
In addition, fat programs designed to patch code or resources can improve performance by reducing the work of the Mixed Mode Manager. Since a fat program can contain both CFM-based code and classic 68K code, it can execute whichever code is necessary to avoid a mode switch.
Of course, if you installed this system on a 68k, then it probably does contain a lot more 68k code running under emulation than if you had installed it on a PowerPC system, as well as lacks mode-specific extensions or whatever, so I wouldn't recommend using this.