Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!uakari.primate.wisc.edu!aplcen!haven!udel!princeton!phoenix!jwbirdsa From: jwbirdsa@phoenix.Princeton.EDU (James Webster Birdsall) Newsgroups: comp.sys.ibm.pc Subject: Re: Ever heard of a mac emulator? Message-ID: <11074@phoenix.Princeton.EDU> Date: 25 Oct 89 17:05:08 GMT References: <23793@sequent.UUCP> Reply-To: jwbirdsa@phoenix.Princeton.EDU (James Webster Birdsall) Distribution: usa Organization: Princeton University, NJ Lines: 53 In article <23793@sequent.UUCP> coryc@sequent.UUCP (Cory Carpenter) writes: >Has anyone out there in the IBM PC world heard of an emulator for >XT-class machines that runs Macintosh software? > >----------------------------------------------------------------------- >| Cory R. Carpenter | "Please fasten your | There was an XT emulator for the Mac (which, as I recall, was called the SoftPC and was a failure for reasons I'll get to below). But I don't think anybody has written a Mac emulator for the PC... It is possible to run binaries for one chip on another chip by writing what amounts to a machine-language interpreter, which reads the opcodes (for the 8088, in this case) and performs the indicated operation using the opcodes of its own processor (the 68000). Of course, this usually has to be coupled with an OS faker, which emulates the functions of the OS of the emulated machine. Plus, you're having to manage a virtual memory space (you have to feed the binary the sort of addresses it's looking for while keeping track of where you've actually put those bytes), and, in the case of emulating a DOS machine, you have to be prepared for programs which want direct access to the hardware. In practice, nobody has ever actually done this. The SoftPC would only run with well-behaved programs and, in any case, interpreting machine language is INCREDIBLY slow. The Amiga has a far more intelligent approach with the BridgeCard, which has an actual Intel 8088 with its own memory and some associated hardware like communication ports and several expansion slots (!). In this case, the problem is reduced to getting the 8088 binaries to the 8088 (not a problem, since the BridgeCard comes with a floppy drive which connects directly to it) and getting the display onto the Amiga's screen. The 8088 runs standard DOS, so not even an OS faker is required. The 8088 can even have its own hard drive, since it has standard XT expansion slots. Some additional fooling around is required in order to get the two halves of the machine to share hard drives, but software to do this is already available. Whew... sorry to go on for so long. The summary is: software emulators are nearly impossible to write, don't do everything, and are so slow as to be tough to use. Hardware hacks are much easier, but I don't think anybody has done a Mac-on-a-board for the PC, especially with the way Apple is about the Mac ROMs... -- James W. Birdsall jwbirdsa@phoenix.Princeton.EDU jwbirdsa@pucc.BITNET ...allegra!princeton!phoenix!jwbirdsa Compu$erve: 71261,1731 "For it is the doom of men that they forget." -- Merlin