Nonpaged Pool Memory

what distinguishes Paged Pool and NonPaged Pool memory? The first difference is that Paged Pool is exactly what its name implies - it can be paged out. The NonPaged Pool cannot be paged out. Drivers use the NonPaged Pool for many of their requirements because they can be accessed at any Interrupt Request Level (IRQL). The IRQL defines the hardware priority at which a processor operates at any given time (there's a link to a document covering Scheduling, Thread Context and IRQL's in the Additional Resources section at the end of this post).

Getting back to our Pool Resources, it is important to remember that these resources are finite. The table below outlines some sample maximum values for Paged / NonPaged Pool on x86 systems that are not configured with the /3GB switch in the system's boot.ini file. We'll cover /3GB and its effects on memory in a future post. We'll also cover Kernel Changes to Windows Vista separately. It's important to note that x64 systems don't suffer from the same Virtual Address Space limitations!

Windows 2000

System RAM	NonPaged Max	Paged Max	Paged Max (TS)
512 MB	131 MB	264 MB	160 MB *
1024 MB	212 MB	268 MB	160 MB *
1536 MB	256 MB	340 MB	160 MB *
2048 MB	256 MB	340 MB	160 MB *

* If Terminal Services is installed on Windows 2000, Paged Pool is lowered down to 160 MB unless a registry change is made to the server to set the Paged Pool Size to its maximum value (see below).

Windows 2003 SP1

System RAM	NonPaged Max	Paged Max
512 MB	125 MB	184 MB
1024 MB	202 MB	168 MB
1536 MB	254 MB	352 MB
2048 MB	252 MB	352 MB

On Windows 2003 systems, Terminal Services are enabled by default.

On both Windows 2000 and Windows 2003, the HKLM\System\CurrentControlSet\Control\Session Management\Memory Management\PagedPoolSize value can be set to 0xFFFFFFFF (or resetting the value to 0) to ensure that the Virtual Address Space used for Paged Pool is maximized.

Also - here's the theoretical maximums for pre-Vista Operating Systems:

Region	IA-64	x64	x86
Process Address Space	7152 GB	8192 GB	2 to 3 GB*
Paged Pool	128 GB	128 GB	470 to 650 MB
NonPaged Pool	128 GB	128 GB	256 MB

http://blogs.technet.com/b/askperf/archive/2007/03/07/memory-management-understanding-pool-resources.aspx


For server runing Exchange 2003

The following table displays the matrix of evaluations used by the Exchange Server Analyzer to determine whether this value is out-of-bounds for a specified Exchange server. If the conditions in the following table are matched, a warning is displayed.

Operating System	Boot.ini Setting	Current Non-Paged Pool is
Microsoft Windows 2000 Advanced Server	/3GB	100 MB or more
Microsoft Windows 2000 Server or Advanced Server	None	200 MB or more
Microsoft Windows Server™ 2003	/3GB	100 MB or more
Microsoft Windows Server 2003	None	200 MB or more

The PoolNonpagedBytes key value is the size, in bytes, of the kernel memory non-paged pool. This is an area of physical system memory for objects that cannot be written to disk even when they are not being used. This value for this key is the last observed value. On a healthy Exchange server, unless a backup or restore is occurring, there should be no more than 85 MB of non-paged pool memory being used.

http://technet.microsoft.com/en-us/library/aa996269%28EXCHG.80%29.aspx