Relative
Performance
Log Problem Size
D$
E$
32-bit VA limit
hw PA limit
Figure 1–1 Typical Performance versus Problem Size Curve
Beyond the 32–bit virtual address limit, applications programmers can still handle
large problem sizes — usually by splitting the application data set between primary
memory and secondary memory, for example, onto a disk. Unfortunately,
transferring data to and from a disk drive takes a longer time, in orders of
magnitude, than memory-to-memory transfers.
Today, many servers can handle more than 4 Gbytes of physical memory. High-end
desktop machines are following the same trend, but no single 32–bit program can
directly address more than 4 Gbytes at a time. However, a 64–bit application can use
the 64-bit virtual address space capability to allow up to 18 Ebytes (1 Exabyte is
approximately 10
18
bytes) to be directly addressed; thus, larger problems can be
handled directly in primary memory. If the application is multithreaded and scalable,
then more processors can be added to the system to speed up the application even
further. Such applications become limited only by the amount of physical memory in
the machine.
It might seem obvious, but for a broad class of applications, the ability to handle
larger problems directly in primary memory is the major performance benefit of
64-bit machines.
4
A greater proportion of a database can live in primary memory.
4
Larger CAD/CAE models and simulations can fit in primary memory.
4
Larger scientific computing problems can fit in primary memory.
4
Web caches can hold more in memory, reducing latency.
Beyond Large Address Spaces
Other compelling reasons why you might want to create 64–bit applications include:
2
Solaris 64-bit Developer’s Guide ♦ February 2000
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