64 bit Editions of Windows Evaluation Guide - Technology and Trends

64 bit Editions of Windows Background Information �
Another major driving force to the 64 bit Editions of Windows is the commitment by Independent
Software Vendors (ISVs) to develop their applications to leverage the capabilities of 64 bit
Editions of Windows.
32 bit versus 64 bit Applications
The 64 bit Editions of Windows include features that overcome many of the limitations of the 32
bit Windows system. For example, the 64 bit Editions of Windows support far more physical
memory than a 32 bit operating system (32 bit Windows supports 4 gigabytes of memory, while
the 64 bit Editions of Windows supports 16 terabytes of memory). Increased physical memory
allows more applications to run simultaneously and remain completely resident in the system's
main memory. This reduces or eliminates the performance penalty of swapping pages to and
from disk.
Win32-based applications run on the 64 bit Editions of Windows using an emulation layer.
However, 32 bit applications will run significantly slower on the 64 bit Editions of Windows than on
32 bit systems. Running 32 bit applications is not recommended for organizations looking for the
best price and performance benefits of the 64 bit Editions of Windows. In summary, performance
for 32 bit applications will be greater on 32 bit hardware.
In general, only applications that require the increased power of 64 bit technology should be
developed in 64 bit and run on a 64 bit Itanium processor. The 32 bit emulator in the 64 bit
Editions of Windows is designed to run 32 bit productivity applications needed by software
developers and administrators, not to run 32 bit applications for the end user.
Microsoft is working with Independent Software Vendors in conjunction with the 64 bit product
development programs to develop software that will run unmodified on both 32 bit and 64 bit
Editions of Windows-based computers. This will give companies the ability to add 64 bit Editions
of Windows-based systems to existing networks without changing the 32 bit applications currently
in use.
As organizations begin to deploy the 64 bit Editions of Windows, most of the applications they run
on 32 bit Windows-based computers will need to be ported over to the 64 bit environment,
allowing applications to leverage the new benefits of the 64 bit platform. Microsoft provides the
Software Development Kit (SDK) and the Driver Development Kit (DDK) to easily migrate
applications to the new 64 bit Editions of Windows on Itanium Processor systems. (More
information about Microsoft’s SDK and DDK is provided in the section “Porting Your Applications
to 64 bit”.) Microsoft also supports migrating applications using the 64 bit Editions of Windows
data model. This data model provides the capability to write a single-source code that can run on
both 32 bit and 64 bit computers.
� 64 bit Editions of Windows Evaluation Guide 2-5