Xref: utzoo comp.sys.mac.programmer:18644 comp.sys.mac.misc:5054 Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!zaphod.mps.ohio-state.edu!rpi!mts.rpi.edu!Garance_Drosehn From: Garance_Drosehn@mts.rpi.edu (Garance Drosehn) Newsgroups: comp.sys.mac.programmer,comp.sys.mac.misc Subject: Re: ROM in RAM Message-ID: Date: 31 Oct 90 20:29:29 GMT Distribution: usa Organization: Rensselaer Polytechnic Inst. Lines: 35 References:<1990Oct31.032509.265@bushido.uucp> <1990Oct31.162230.3292@engin.umich.edu> In article <1990Oct31.162230.3292@engin.umich.edu> mystone@mondo.engin.umich.edu (Dean Yu) writes: > On the Macintosh, ROM is at least as fast as RAM, probably faster, so > that's one reason not to bother. Then there is the size of the ROM. If > you copied the ROM into RAM, you'd suck up anywhere between 128K to 512K > of your memory. (Not that it really matters these days, but I like lots > of free RAM.) > The last reason, and probably the most important is that this would break > every single come-from patch, since they check the return address on the > stack, and of course, moving ROM to RAM would cause these return > addresses to change. Well, you have to be wrong on that last point, because I have an accelerator that does just want the original poster talked about. It copies the ROM's into RAM at startup time (eating up a chunk of RAM), and everything works perfectly fine. The CDEV for the accelerator (an Irwin Magnetics XL25) has this as an option, so if something didn't work you can turn it off. I've never tripped across a bug where turning this off (and rebooting) made any difference. I don't have a clue how they do it, of course, but it is done. Perhaps they do some special trick to work with the patches you mention. On the accelerator this trick of copying ROM into RAM makes sense, because it's using the ROM's from a plain SE, but the accelerator is running a 25Mhz 68020 with 70ns memory in it. Copying the ROM into RAM does speed things up in that case. I doubt it would make any difference for a regular (non-accelerated) Mac. And since you have to have an official Apple ROM in the machine for this to work, it isn't any problem legally. Garance_Drosehn@mts.rpi.edu ITS Systems Programmer Rensselaer Polytechnic Institute; Troy, NY. USA