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Virtualisation planning process : memory configuration maximums.

Today’s  challenge for a virtualization admins it’s to provision memory requirements within the guest for unique workloads,  paying attention to the host environment.

Although today, memory is relatively cheap, it may not be the case in the future and we also need to take in consideration the host maximums, as this will impact what OS would be available for a guest virtual machine as well as the aggregated impact on the host. It is notorios that system/applications that are replacing older servers running W2K/W2K3 to now require more resources(RAM, CPU, Disk, Network )  than the previous systems/apps.

It is important to pay special attention to the memory limits, requirements and aggregate memory capacity with insight to future needs.

Limits on memory and address space vary by platform, operating system, and by whether the IMAGE_FILE_LARGE_ADDRESS_AWARE value of the LOADED_IMAGE structure and 4-gigabyte tuning (4GT) are in use. IMAGE_FILE_LARGE_ADDRESS_AWARE is set or cleared by using the /LARGEADDRESSAWARE linker option.

Limits on physical memory for 32-bit platforms also depend on the Physical Address Extension (PAE), which allows 32-bit Windows systems to use more than 4 GB of physical memory.

Memory and Address Space Limits

The following table specifies the limits on memory and address space for supported releases of Windows. Unless otherwise noted, the limits in this table apply to all supported releases.

Memory type Limit in 32-bit Windows Limit in 64-bit Windows
User-mode virtual address space for each 32-bit process 2 GBUp to 3 GB with IMAGE_FILE_LARGE_ADDRESS_AWARE and 4GT 2 GB with IMAGE_FILE_LARGE_ADDRESS_AWARE cleared (default)4 GB with IMAGE_FILE_LARGE_ADDRESS_AWARE set
User-mode virtual address space for each 64-bit process Not applicable With IMAGE_FILE_LARGE_ADDRESS_AWARE set (default):x64:  8 TBIntel IPF:  7 TB2 GB with IMAGE_FILE_LARGE_ADDRESS_AWARE cleared
Kernel-mode virtual address space 2 GBFrom 1 GB to a maximum of 2 GB with 4GT 8 TB
Paged pool Limited by available kernel-mode virtual address space or the PagedPoolLimit registry key value.Windows Vista:  Limited only by kernel mode virtual address space. Starting with Windows Vista with Service Pack 1 (SP1), the paged pool can also be limited by the PagedPoolLimit registry key value.Windows Home Server and Windows Server 2003:  530 MBWindows XP:  490 MBWindows 2000:  350 MB 128 GBWindows Server 2003 and Windows XP:  Up to 128 GB depending on configuration and RAM.Windows 2000:  Not applicable
Nonpaged pool Limited by available kernel-mode virtual address space, the NonPagedPoolLimit registry key value, or physical memory.Windows Vista:  Limited only by kernel mode virtual address space and physical memory. Starting with Windows Vista with SP1, the nonpaged pool can also be limited by the NonPagedPoolLimit registry key value.Windows Home Server, Windows Server 2003, and Windows XP/2000:  256 MB, or 128 MB with 4GT. 75% of RAM up to a maximum of 128 GBWindows Vista:  40% of RAM up to a maximum of 128 GB.Windows Server 2003 and Windows XP:  Up to 128 GB depending on configuration and RAM.Windows 2000:  Not applicable
System cache virtual address space (physical size limited only by physical memory) Limited by available kernel-mode virtual address space or the SystemCacheLimit registry key value.Windows Vista:  Limited only by kernel mode virtual address space. Starting with Windows Vista with SP1, system cache virtual address space can also be limited by the SystemCacheLimit registry key value.Windows Home Server, Windows Server 2003, and Windows XP/2000:  860 MB with LargeSystemCache registry key set and without 4GT; up to 448 MB with 4GT. Always 1 TB regardless of physical RAMWindows Server 2003 and Windows XP:  Up to 1 TB depending on configuration and RAM.Windows 2000:  Not applicable

 —

Physical Memory Limits: Windows Server 2008 R2

The following table specifies the limits on physical memory for Windows Server 2008 R2. Windows Server 2008 R2 is available only in 64-bit editions.

Version Limit in 64-bit Windows
Windows Server 2008 R2 Datacenter 2 TB
Windows Server 2008 R2 Enterprise 2 TB
Windows Server 2008 R2 for Itanium-Based Systems 2 TB
Windows Server 2008 R2 Foundation 8 GB
Windows Server 2008 R2 Standard 32 GB
Windows HPC Server 2008 R2 128 GB
Windows Web Server 2008 R2 32 GB

 —-

Physical Memory Limits: Windows Server 2008

The following table specifies the limits on physical memory for Windows Server 2008. Limits greater than 4 GB for 32-bit Windows assume that PAE is enabled.

Version Limit in 32-bit Windows Limit in 64-bit Windows
Windows Server 2008 Datacenter 64 GB 1 TB
Windows Server 2008 Enterprise 64 GB 1 TB
Windows Server 2008 HPC Edition Not applicable 128 GB
Windows Server 2008 Standard 4 GB 32 GB
Windows Server 2008 for Itanium-Based Systems Not applicable 2 TB
Windows Small Business Server 2008 4 GB 32 GB
Windows Web Server 2008 4 GB 32 GB

 —–

Physical Memory Limits: Windows Server 2003

The following table specifies the limits on physical memory for Windows Server 2003. Limits over 4 GB for 32-bit Windows assume that PAE is enabled.

Version Limit in 32-bit Windows Limit in 64-bit Windows
Windows Server 2003 with Service Pack 2 (SP2), Datacenter Edition 128 GB64 GB with 4GT IA64 2 TBX64 1 TB
Windows Server 2003 with Service Pack 2 (SP2), Enterprise Edition 64 GB IA64 2 TBX64 1 TB
Windows Storage Server 2003, Enterprise Edition 8 GB Not applicable
Windows Storage Server 2003 4 GB Not applicable
Windows Server 2003 R2 Datacenter EditionWindows Server 2003 with Service Pack 1 (SP1), Datacenter Edition 128 GB16 GB with 4GT 1 TB
Windows Server 2003 R2 Enterprise EditionWindows Server 2003 with Service Pack 1 (SP1), Enterprise Edition 64 GB16 GB with 4GT 1 TB
Windows Server 2003 R2 Standard EditionWindows Server 2003, Standard Edition SP1Windows Server 2003, Standard Edition SP2 4 GB 32 GB
Windows Server 2003, Datacenter Edition 128 GB16 GB with 4GT 512 GB
Windows Server 2003, Enterprise Edition 32 GB16 GB with 4GT 64 GB
Windows Server 2003, Standard Edition 4 GB 16 GB
Windows Server 2003, Web Edition 2 GB Not applicable
Windows Small Business Server 2003 4 GB Not applicable
Windows Compute Cluster Server 2003 Not applicable 32 GB
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