🚀 go-pugleaf

ntaib@silver.ucs.indiana.edu (Iskandar Taib) writes:
> davidsen@crd.ge.com (bill davidses writes:
                                                              
>>  The truth is that Mac applications are 32 bit, and DOS applications
>>are 16 bit. A comparison of UNIX 32 bit applications would be more      
>>correct, if they were just comparing the processors.                      
                                                                       
>Well, if this is so, how do the apps run on Mac Pluses? And why is    
>32 bit adressing an option under System 7?   
Part of the answer is in the CPUs Mac and IBM used. Here is part of
my Mac & IBM info article {Arcived on Sumex (36.44.0.6) in the /info-mac/report
directory as mac-ibm-compare.txt}

IBM     ALU  Registers    External    cache    Features/
CPU                     bus  address           Notes
 8088   16      16       8     20      ?      {197?-1989}
 8086   16      16      16     20      ?      {197?-1989}
80286   16      16      16     24      ?      Protected Mode & segmenting
80386   32      32      32     32      ?      MMU & 32-bit Protected Mode 
...
MAC     ALU  Registers    External    cache*   Features/
CPU                     bus  address           Notes
68000   16      32      16     24      none    {1984-1993}
68020   32      32      32     32     i; 256   {1987-1992}
...
Note the bit of the Registers and the addresses.  The 32-bits in the 68000 
register and 24 bits in the address allowed programers to write 24-bit code 
and still allow for 32-code compability.  {That's at least what a Apple/IBM
dealer says and he hates the Mac} The problem is some code is
designed around the 68000 and old OSes and is only 24-bit and so does not
run in 32-bit mode. {System 7.x was the first non-UNIX OS to have 32-bit
addressing, ALL older system back to 4.1 are 24-bit only though they allowed 
for 32-bit code to run} So, all Mac Apps are NOT 32-bit but they ARE 24-bit
{Very badly writen programs did strange things with the higher 8-bits that
Apple said not to do, as a result these programs bomb on the 68020 and higher
and with the newer OS which checked the addressing calls.}

Hope that clears some of the confusion.