Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!think.com!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!dsinc!widener!ukma!memstvx1!utkcs2!emory!swrinde!elroy.jpl.nasa.gov!ames!pasteur!dog.ee.lbl.gov!lbl.gov!jnmoyne From: jnmoyne@lbl.gov (Jean-Noel MOYNE) Newsgroups: comp.sys.amiga.emulations Subject: Re: Mac-system 7.0 Message-ID: <13651@dog.ee.lbl.gov> Date: 29 May 91 01:15:15 GMT Organization: Lawrence Berkeley Laboratory Lines: 37 X-Local-Date: Tue, 28 May 91 18:15:15 PDT References:<4150@jethro.Corp.Sun.COM> <1991May22.090222.2054@bernina.ethz.ch> <471@regina.uregina.ca> <08069.AA08069@babylon.rmt.sub.org> <1101@sys.uea.ac.uk> In article <1101@sys.uea.ac.uk> cmp9133@sys.uea.ac.uk (A.C. Lock) writes: > >> One company (GVP, I think) is now selling "economy" 68030 > >> accelerator cards, with this special no-mmu 68030. > > >Nope, not GVP. > > CSA are manufacturing cheap versions of their Mega Midget Racer cards which do > not contain a MMU, which seems rather silly to me, since it means that memory > access to chip ram is going to be slow since you won't be able to map this > memory using the MMU to 32 bit ram. > > Adam No no no no no ... Let me explain, you don't want to map CHIP memory anywhere, CHIP memory is slow, because it is chip memory which means it is accessed by other co-processors (DMA for guys like the blitter et al.). On the other hand, the ROMS are slower than 32-RAMs, first because they're ROMs and also because they're 16 bits. Since the CPU is the only one to access them, it is nice to be able to use a MMU to map the ROMs (_not_ the CHIP memory!) into fast 32bits RAM. It is true that this unability will make quite a difference on most of the common operations, since mapping the ROMs in fast RAM does the trick, as far as most acceleration goes. JNM --- #include JNM: jnmoyne@lbl.gov - The postmaster allways pings twice (soon in your mailbox!)