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2.1 Migrating to a 64-bit platform
With the addition of 64-bit computing to the xSeries platform you can now run
large scale, mission-critical applications with the x455. The Itanium 2 processor
is suitable for the next generation of high-end applications that will take
advantage of its performance benefits particularly with regards to its flat memory
addressable space, with a theoretical addressable memory limit of 16 EB
(Exabytes).
Migrating existing 32-bit applications can be a time-consuming and complex
process particularly for large-scale mission-critical applications. It is also
acknowledged that some applications will never need the power that 64-bit
processing offers. To assist with this transition and offer backwards compatibility,
the Itanium 2 offers support for IA-32 applications.
In addition, Microsoft has introduced an IA-32 Execution Layer software driver to
further enhance 32-bit support on Windows Server 2003. The driver works by
translating IA-32 code into native Itanium architecture code before it is executed.
It is available from:
http://www.microsoft.com/windowsserver2003/64bit/ipf/ia32el.mspx
A similar driver for Linux is also planned.
To fully take advantage of 64-bit computing, it is important that your existing
32-bit applications are re-written and/or recompiled correctly. Using the 32-bit
compatibility mode of the Itanium 2 or simply recompiling will not yield the
potential benefits. In some cases it will even lead to poorer performance.
32-bit binaries (that is, those that run on Pentium and Xeon processor-based
systems) should execute on Itanium 2 without modification. In fact, both 32-bit
and 64-bit binaries can run simultaneously on the same processor. This allows a
system that is only partially converted to 64 bits to run on the x455. However,
unless the applications are recompiled, 32-bit applications will run slower on the
Itanium 2 because of the emulation overhead and an inability to take advantage
of all the benefits the 64-bit platform offers.
The advantages that 64-bit offers over 32-bit are realized most for applications
that can take advantage of its large addressable flat memory, ability to execute
instructions in parallel, and raw computational ability particularly for applications
that use floating point calculations.
Before migrating, you need to consider many factors. Below are some of these
considerations:
Does your current operating system support 64-bit hardware?
IBM Eserver xSeries 455 Planning and Installation Guide
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