On Dec 11, 2006, at 10:15 AM, Patrick Welche wrote:
>> Also, there are only a few 64-bit architectures that can make use  
>> of true
>> 64-bit addressing.  While the compiler may allow 64-scalar  
>> addressing in the
>> source code, somewhere in the build process, the address is  
>> usually munged
>> down to the size of the MMU quantum which can be 36-bit, 40-bit or  
>> 56-bit
>> depending on architecture.
>
> So going further off-topic - what is the size of a "word"? I think  
> it is
> the same as sizeof(void *) so I would get 64, but should I get  
> 36/40/56 ?

The term "word" is highly overloaded, but many people consider a word  
to be two bytes, which means it will always be 16-bits in size (at  
least if you have 8-bit bytes; PDP users need not apply).  Other  
people consider the size of the word to be the preferred native  
register size, which is commonly either 32 or 64 bits in size in  
modern CPUs.

The bizarre sizes quoted above for MMU sizes appear due to the  
strange and wonderful history of the x86 architecture; almost all  
other platforms have a more sane MMU design.

-- 
-Chuck