64-Bit System

[RateU]

What's the minimum requirement (hardware and OS) for building a 64-Bit System?

[ZiNgA BuRgA]

Do you mean, run a 64-bit OS?
If so, all you need is a x64 capable CPU - pretty much most CPUs made in the last 6 years support x64, starting with the AMD64 and Pentium 4 Prescott lines (with the exception of some Intel Atom CPUs, IDK about Bobcat).
In terms of recommended requirements, you'll probably want to consider if you have enough RAM, since 64-bit will consume more than 32-bit (so, for a low end VPS, 32-bit is probably better in most cases).

[RateU]

Does the 32-bit system (normally) has an ability to save a number to the max value of the Int Unsigned data type, Yumi?

[ZiNgA BuRgA]

Are you refering to PHP?
I'm not sure what MySQL does - their integer types are probably fixed (but you can verify from the documentation).
The traditional definition of an integer is 32-bits long, which is probably what MySQL uses.

PHP's integer type is always signed, so a 32-bit PHP will only be able to use signed 32-bit integers (anything outside the range get auto-converted to double precision float).  So in this case, it can't fully address the range of a 32-bit unsigned integer (without using floats).

[RateU]

Ah, yes. Thank you very much for the explanation, Yumi