Hi Guys,

 to busy during the last weeks to really work on the Blog.

During a lot of partner / customer meetings people are asking if virtualisation of XenApp is the way to go.
One of the arguments against it is to use the Windows PAE switch to allow Windows to use more memory.

Well this will prevent you from using all the great features of virtualisation. But it’s also completely wrong from technical perspective.

PAE is an Intel-provided memory address extension that enables support of greater than 4 GB of physical memory for most 32-bit (IA-32) Intel Pentium Pro and later platforms. This article provides information to help device driver developers implement Windows drivers that support PAE.

Microsoft supports Physical Address Extension (PAE) memory in Microsoft Windows 2000, Windows XP, and Windows Server 2003 products:

Operating system Maximum memory support with PAE
Windows 2000 Advanced Server 8 GB of physical RAM
Windows 2000 Datacenter Server 32 GB of physical RAM
Windows XP (all versions) 4 GB of physical RAM*
Windows Server 2003 (and SP1), Standard Edition 4 GB of physical RAM*
Windows Server 2003, Enterprise Edition 32 GB of physical RAM
Windows Server 2003, Datacenter Edition 64 GB of physical RAM
Windows Server 2003 SP1, Enterprise Edition 64 GB of physical RAM
Windows Server 2003 SP1, Datacenter Edition 128 GB of physical RAM

* Total physical address space is limited to 4 GB on these versions of Windows.

PAE is supported only on 32-bit versions of the Windows operating system. 64-bit versions of Windows do not support PAE. For information about device driver and system requirements for 64-bit versions of Windows, see 64-bit System Design.Although support for PAE memory is typically associated with support for more than 4 GB of RAM, PAE can be enabled on Windows XP SP2, Windows Server 2003, and later 32-bit versions of Windows to support hardware enforced Data Execution Prevention (DEP).
Operating System Support. The PAE kernel is not enabled by default for systems that can support more than 4 GB of RAM.

To boot the system and utilize PAE memory, the /PAE switch must be added to the corresponding entry in the Boot.ini file. If a problem should arise, Safe Mode may be used, which causes the system to boot using the normal kernel (support for only 4 GB of RAM) even if the /PAE switch is part of the Boot.ini file.

The PAE mode kernel requires an Intel Architecture processor, Pentium Pro or later, more than 4 GB of RAM, and Windows 2000, Windows XP, or Windows Server 2003.

The PAE kernel can be enabled automatically without the /PAE switch present in the boot entry if the system has DEP enabled (/NOEXECUTE switch is present) or the system processor supports hardware-enforced DEP. Presence of the /NOEXECUTE switch on a system with a processor that supports hardware-enforced DEP implies the /PAE switch. If the system processor is capable of hardware-enforced DEP and the /NOEXECUTE switch is not present in the boot entry, Windows assumes /NOEXECUTE=optin by default and enables PAE mode. For more information, see the topic “Boot Options in a Boot.ini File” in the Windows DDK.
Link:  http://www.microsoft.com/whdc/system/platform/server/PAE/PAEdrv.mspx