Psst! EM64T Is Here
The Nocona core supports the EM64T enhancement, which is compatible with AMD64. The server version of Windows is already available as a 64 bit edition.
The second interesting feature of the Nocona processor is the 64 bit enhancements, which Intel groups together under the heading Extended Memory 64 technology, or EM64T for short. As the Itanium II, Intel's "proper" 64 bit model, absolutely demands its own Windows, along with adapted 64 bit applications, Intel has preferred to accept the fact that EM64T is compatible with AMD64. As a result, to be specific, the immense number of 32 bit applications can continue to be operated - a not entirely insignificant factor. Certainly, the technology is implemented in a different way at Intel compared to its competitor AMD, but this should not make any difference with Windows. The activation of the 64 bit mode does, in practice, have one noteworthy disadvantage: the floating-point unit is thereby rendered inoperable (even for AMD).
However, according to Intel, the main reason for introducing EM64T (x86-64) is not the higher operating speed, which is made possible by the processing bandwidth, but the possibility of addressing up to 281 teraBytes of RAM. Up to now, as a general rule, 4 GB has been the limit, though up to 12 GB was already feasible with some chipsets.
Expanding memory of this magnitude has, however, been impossible to date, as firstly, memory modules of over 2 GB per DIMM are very unusual and, secondly, only 50 of the 64 data lines are external with Xeon, not to mention the limited number of DIMM sockets. In that respect, there remains a technically feasible limit of 39 teraBytes.
Both Intel and Microsoft are currently displaying great ambition when it comes to introducing 64 bit technology on a broad front. Intel, according to its own statistics, has already sent 4,000 systems to developers for this purpose. At the same time Microsoft is providing the 64 bit edition of Windows XP Professional for download free of charge as a 360 day demo version. Well, if that is not a reason for changing over!.