[comp.sys.mac.hardware] MODE32 ???

bangrazi@ctron.com (Anthony Bangrazi) (06/27/91)

Could someone please tell me what MODE32 is supposed to do? I've got an SE/30.
Do I need MODE32? Oh, I use system 7.0, too. Thanks for the help.

- Anthony

mjkobb@media-lab.media.mit.edu (Michael J Kobb) (06/28/91)

In article <1738@balrog.ctron.com> bangrazi@ctron.com writes:
>Could someone please tell me what MODE32 is supposed to do? I've got an SE/30.
>Do I need MODE32? Oh, I use system 7.0, too. Thanks for the help.

Hi,

  On older Macs in the Mac-II series (SE/30, Mac II, Mac IIx, Mac IIcx), you
can't use the 32-bit addressing feature of System 7, because the ROM isn't
"clean", i.e. the programmers used the high byte of the address for something
other than addresses, which does bad things.  This was fixed on the new Macs.

  MODE 32 is an init/cdev combination that allows the Mac to run in 32-bit
mode, just as a "clean" Mac does.

  What 32-bit addressing allows you to do is access more than the 16Mb of
address space that 24-bit addressing lets you use.  So, you could put 4Mb
SIMMS in your Mac IIx (you need a special SIMMS, I think), and use 32Mb of
physical RAM, and tons o' virtual.  With 24-bit addressing, you're limited to
8Mb physical, and 14Mb virtual minus 1Mb for every NuBus card installed.

  I've been using it for a while, and it seems quite compatible, system-wise.
The problems arise with non-32-bit clean applications like ATM, Director,
SuperPaint, etc.  These cause interesting bombs...

Hope this helps!