Re: Macintosh LC...need info on this =) TIA

[Matt Jenkins <mdj@bilby.cs.rmit.edu.au>]

Roy and/or Janet Miller <millers@inetnebr.com> wrote:
> frankc wrote:

>> I think to keep in the spirit of early Apple machines maybe we should
>> service the needs of users of older Macs.  I do not own any newer Macs,
>> but I do own some of the older 8/16 bits versions (Is the 68000 8-bit?)

> The 68000 is generally rated as a 16/32 bit chip (kinda like the 8088 was an
> 8/16 bit chip)

I think you mean 32/24 bit chip. The 68000 has real 32 bit instructions, real 32 bit
registers, etc. It is indeed a 32 bit processor. The only 'problem' is that the address
bus of the thing can only use 24 bits to address memory, and hence you're limited to
16mb of ram on a 68k.

This is where the Mac concept of '32-bit clean' apps comes from. Many old applications
(including MacOS 6.x) used to hide data in the high order byte of the 68k's address
registers for speed, since only 24 bits were actually used for addressing. This is why
68030 Macs (eg. Mac IIci, IIsi, LCIII) have the 32bit addressing switch in the control
panel, so you can disable 32bit addressing and run older applications or older System
software. Starting with the 68040 machines (Quadra, Centris, etc) the CPU's could no
longer do this, and hence you couldn't run any OS older than 7.0, and dozens of old
classic Mac apps also.

Hope this clears things up - too much Mac lore for a II news group :)

-- 
              Matt(hew) Jenkins. Computer Science (RMIT Bundoora)
                           email: mdj@cs.rmit.edu.au
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