Why Windows 7 64-bit requires that much RAM?

My guess is a 64 bit word takes twice the space as a 32 bit word even if only the first 32 bits (or even one bit only) are used. Playing to the angels Les Paul (1915-2009)

What you are reffering to is the minumem ram requirement is higher beyond that the double amount does not apply. As most Vista systems now have 2-3gb and some even 4, that does not mean that the 64 bit needs 4, 6 or 8gb. However if you have 4gb or more 64bit, is required to be able to use all of it. 64bit is not designed with extra features like you would get going from Basic to Ultimate, it's more efficient at transferring data and able to to handle more ram then 32bit.

Yes, it will require more memory from time-to-time, but it's not cut & dried. The reason M$ is suggesting at least twice as much memory is to allow for adequate contingencies since your 64-bit Windows comprises 32-bit libraries as well as 64-bit libraries for 32-bit app compability ... see below. "The main disadvantage of 64-bit architectures is that relative to 32-bit architectures the same data occupies more space in memory (due to swollen pointers and possibly other types and alignment padding). This increases the memory requirements of a given process and can have implications for efficient processor cache utilization. Maintaining a partial 32-bit model is one way to handle this and is in general reasonably effective. In fact, the highly performance-oriented z/OS operating system takes this approach currently, requiring program code to reside in any number of 32-bit address spaces while data objects can (optionally) reside in 64-bit regions." http://en.wikipedia.org/wiki/64-bit Windows 7 News!

About the same as windows xp for 32 bit (128mb) but for 64 bit probabaly only 512-1 gb minimum. But It would be slow so id go for about 2gb at least