68k system on PowerPC?

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68k system on PowerPC?

Post by ray » 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.
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Re: 68k system on PowerPC?

Post by Turboladdade » 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.
I am now telling the computer exactly what it can do.
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