32 bit vs 64 bit computer ?

[Joe Griffin]

Yoon Jae Ho,

>I want to know the exact definition of 
>the 32 bit computer (PC ) vs 64 bit computer.
>and Why we can't make 128 bit computer for
>long time ?

The term "64 bit computer" is usually
used for one of two types:
LP64 ..... longs and pointers are 64 bits 
           (example is an Intel Itanium).
ILP64 .... Integer, Reals, longs and pointers are
           64 bits (example is a CRAY)

LP64 systems allow for high address ranges.
IPL64 allows for a high address range, and
greater accuracy of calculations.

To answer why can't we make 128 bit computer,
I must ask, why would you want to?

2^128 is a very big number.  I could not see
the need for either that much address space 
or that much precision.

>I don't know how much(the maximum number) 
>the 32 bit computer vs 64 bit makes exact
> calculation without error.
> and With different architecture PCs - for
> example AMD, Intel, MAC cpu , Is it possible
> to communate the calculatiton results each other ?

On a 32 bit system like Intel/AMD chips, Real data
uses the following:
1 bit ..... sign
8 bits .... Exponent (magnitude of number)
23 bits ... Mantissa (accuracy of number)

On a 32 bit system you may have 64 bit reals.  If
so:

1 bit ....  sign
11 bits ... Exponent
52 bits ... Mantissa

>and With same os - for example LINUX, Is it possble
> to make one beowulf Using Alpha(64 bit) & Intel(32 bit) Computers ?

I believe a strict definition of beowulf is commodity 
of the shelf systems.  I don't think Alpha is included there.
But lots of people mean "cluster" when they say beowulf.
You can cluster Alpha and Intel systems, but using 
them together is dependent of the software.

>I mean we can communicate the calculation results with
>each other( 32 bit vs 64 bit) during caluculation with same O.S ?

During the calculations???  I think not.

Regards,
Joe