On Dec 31, 2003, at 12:45 am, Andrew Kershaw wrote:
I have PB100, 140, 145, 160, 165, 165c, 170, 180c, and 190. How do I know which are "32-bit clean" and which aren't?
That's a good question.
It's hard to tell from just looking at the Mac. I guess you could use a tool like TattleTech or Tech Tool figure it out... Anyone else know how to figure it out in a fairly simple manner?
Open the Memory Control Panel, it should have a switch for 24/32-bit mode on 'clean' machines but AFAIK it's disables on 24-bit ROM'd machines and u have to use a 32-bit INIT (Extension) to use 32-bit addressing.
Mode 32 is the extension. There are two versions, one for OS v7.5.x and one for earlier versions.
Basically you can split the 68K machines into three groups. The 68000 machines (128K, Plus, PB100 and others) are 24 bit only. The processor itself is limited to 24 bits so there isn't anything you can do to expand it. A small list (see below) of machines are 32 bit capable but the ROMs are limited to 24 bit. All other 68K machines are 32 bit clean.
Since the early machines could only address 24 bits it didn't matter what the upper 8 bits were in address values. Apple used these upper 8 bits as flags for memory pointers. 68020 and 68030 (and maybe 68040) machines have hardware to let them switch between 24 and 32 bit addressing. In the Mac II this is done with the HMMU chip, in later machines it's done in the PMMU function built into the CPU.
In order to use 32 bit addressing the hardware must support it as all 68020 and later machines do and the ROM must support it. The Mac II, IIx, IIcx and SE/30 have ROMs that don't support 32 bit addressing, all other 68020, 68030 and 68040 machines do have ROMS that support 32 bit addressing. Mode32 is a patch that the OS to support 32 bit addressing. Starting with OS 7.6.1 Mode32 can't work and the machine MUST have 32 bit capable (32 bit clean) ROMs.
So in the list at the top of this message only the PB100 isn't 32 bit clean because it has a 68HC000 and simply cannot address more than 16Mb of memory (8Mb of RAM).
--
Clark Martin
Redwood City, CA, USA
Macintosh / Internet Consulting
"I'm a designated driver on the Information Super Highway"
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