Hardware Reference
In-Depth Information
What we need to make all this work is a 64-bit OS and, more importantly, 64-bit drivers
for all our hardware to work under that OS. Although Microsoft released a 64-bit version
ofWindowsXP,fewcompanies released 64-bit XPdrivers. Itwasn'tuntil WindowsVista
and especially Windows 7 x64 versions were released that 64-bit drivers became plentiful
enough that 64-bit hardware support was considered mainstream.
Note that Microsoft uses the term
x64
to refer to processors that support either AMD64 or
EM64T because AMD and Intel's extensions to the standard IA32 architecture are prac-
tically identical and can be supported with a single version of Windows.
Note
Early versions of EM64T-equipped processors from Intel lacked support for the LAHF and
SAHF instructions used in the AMD64 instruction set. However, Pentium 4 and Xeon DP
processorsusingcoresteppingsG1andhighercompletelysupporttheseinstructions;aBIOS
update is also needed. Newer multicore processors with 64-bit support include these instruc-
tions as well.
The physical memory limits for Windows XP and later 32-bit and 64-bit editions are
shown in
Table 3.5
.
Table 3.5 Windows Physical Memory Limits
The major difference between 32-bit and 64-bit Windows is memory sup-
port—specifically,breakingthe4GBbarrierfoundin32-bitWindowssystems.32-bitver-
sions of Windows support up to 4GB of physical memory, with up to 2GB of dedicated
memory per process. 64-bit versions of Windows support up to 192GB of physical
memory, with up to 4GB for each 32-bit process and up to 8TB for each 64-bit process.
Support for more memory means applications can preload more data into memory, which
the processor can access much more quickly.
