Memory
The most obvious and often mentioned benefit to 64-bit computing is the vastly greater memory addressing space available. Table 1 shows the differences.
General Memory Limits
|
32-Bit
|
64-Bit
|
Total virtual address space (based on a single process)
|
4 GB
|
16 TB
|
Virtual address space per 32-bit process
|
2 GB (3 GB if system
is booted with /3GB switch)
|
4 GB if compiled with /LARGEADDRESSAWARE (2 GB otherwise)
|
Virtual address space per 64-bit process
|
Not applicable
|
8 TB
|
Paged pool
|
47 MB
|
128 GB
|
Non-paged pool
|
256 MB
|
128 GB
|
System Page Table Entry (PTE)
|
660 MB to 900 MB
|
128 GB
|
Physical Memory and CPU Limits
|
32-Bit
|
64-Bit
|
Windows XP Professional
|
4 GB / 1 to 2 CPUs
|
128 GB / 1 to 2 CPUs
|
Windows Server 2003, Standard Edition
|
4 GB / 1 to 4 CPUs
|
32 GB / 1 to 4 CPUs
|
Windows Server 2003, Enterprise Edition
|
64 GB / 1 to 8 CPUs
|
1 TB / 1 to 8 CPUs
|
Windows Server 2003, Datacenter Edition
|
64 GB / 8 to 32 CPUs
|
1 TB / 8 to 64 CPUs
|
Table 1. Memory and Address Comparison of 32-Bit and 64-Bit Windows
Moving to a 64-bit architecture changes the amount of virtual memory that can be directly addressed from 4 GB to 16 terabytes (TB). This 16 TB is, like the 4 GB of 32-bit Windows, divided evenly between user mode processes and kernel mode. Native 64-bit applications have 8 TB of available virtual memory address space.
Beyond virtual memory address space, however, is the very real increase in actual physical memory that is supported under the x64 Editions of Windows.
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