HP ML530 - ProLiant - 128 MB RAM Brief Manual page 5

ProLiant ML530 High-Performance Technologies
figure 4. Hyper-Threading technology
In a multiprocessing system, the OS manages the tasks performed by all processors in
the system. To take advantage of multiple processors, applications must be multi-
threaded, which means they must be designed to be split into multiple streams of
instructions, or threads. The OS can allocate various software threads to run on more
than one processor simultaneously, which results in improved performance. But first, the
OS needs to know the number of available processors so it can distribute the optimum
number of threads among the processors.
The system BIOS counts the number of processors so the OS can create the optimum
number of software threads for better load balancing. A table in the system BIOS
records the number of processors and tags each one as a physical or logical processor.
Figure 5 illustrates the counting order. The system BIOS counts the first logical processor
on each physical processor. Then, in the same sequence, the system BIOS counts the
second logical processor on each physical processor. This ensures that the OS uses
separate physical processors as often as possible to maximize performance.
figure 5. The system BIOS counts processors.
The counting of physical and logical processors can also be used to determine
per-processor license compliance. Using the example in Figure 5, the system with two
processors would exceed the license limit for a two-processor OS if the OS cannot
differentiate between physical and logical processors. For example, Microsoft Windows
2000 Server products counts the logical processors, so it will not use subsequent logical
processors once it reaches the license limit. On the other hand, Windows .NET products
count the physical processors and use all their logical processors. For example,
Windows .NET Standard Server has a two-processor licensing limit. However, in a 2P
system using Xeon processors with Hyper-Threading technology, Windows .NET can get
the benefit of four logical processors. The table that records the processors in the BIOS
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