At this registry location:

HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Executive

create or modify “AdditionalCriticalWorkerThreads” and also “AdditionalDelayedWorkerThreads”, both DWORDs.

For a 32-bit system, I have come to prefer decimal values of 6 times the number of gigs of RAM. So a 1/2G RAM system gets 3, a 4G system gets 24. For a 64-bit system, I use 3 times the number of gigs of RAM.

The above include statements that the maximum value actually used by Windows for these entries is 16. However, the pages are old enough that they do not discuss 64-bit environments; and the second page, the more recent of the two, states that the registry entries exist by default, which they do not.

A major software vendor (which shall now go unnamed) had a page, now taken down, which seemed to at least leave the possibility open that higher numbers may be viable, 64 being recommended by them for a third item otherwise apparently undocumented:

HKLM\SYSTEM\CurrentControlSet\Services\RpcXdr\Parameters\DefaultNumberofWorkerThreads

But just today, I learned of this page:

https://blogs.technet.microsoft.com/josebda/2010/08/27/performance-tuning-guidelines-for-windows-server-2008-r2/

which references this page at Microsoft:

https://msdn.microsoft.com/en-us/library/windows/hardware/dn529134

which contains references for all current Windows Server versions. These touch all of the above and a lot more! Haven’t read them all yet, but will, am thinking to learn lots of interesting things. A quick peruse did reveal that the old hard max of 16 no longer applies, 64 is mentioned, at least in the Server 2008R2 document.

Below is a VBscript, not been updated in a while, which attempts to give an all-around tweak set for the above. Will be working on this soon from that Microsoft page.

' ***************************************
' ******* Optimize Worker Threads *******
' ****************** 2.0 ****************
' ***************************************
' ********* Jonathan E. Brickman ********
' ********* jeb@ponderworthy.com ********
' ***************************************
' ***************************************

' ********** Set up environment *********

Option Explicit

Dim HKEY_LOCAL_MACHINE, strComputer, CPUarch
Dim Return
Dim AddCriticalWorkerThreads, AddDelayedWorkerThreads, DefaultWorkerThreads

HKEY_LOCAL_MACHINE = &H80000002
strComputer = "."

' ********** Find out how much RAM is in machine *******

Dim RAMobj, i, RAMobj2, memTmp1, TotalRAM

Set RAMobj = GetObject("winmgmts:").InstancesOf("Win32_PhysicalMemory")
i = 1
For Each RAMobj2 In RAMobj
	memTmp1 = CDbl(RAMobj2.capacity) / CDbl(1024) / CDbl(1024) / CDbl(1024)
	TotalRAM = TotalRAM + memTmp1
	i = i + 1
Next

Set RAMobj = Nothing
Set RAMobj2 = Nothing

' ******** Get ready for registry operations **********

Dim ObjRegistry, strPath, strValue

Set ObjRegistry = _
    GetObject("winmgmts:{impersonationLevel = impersonate}!\\" _
    & strComputer & "\root\default:StdRegProv")

' ********** Find out whether OS is 32-bit or 64-bit **********

' HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Environment\PROCESSOR_ARCHITECTURE
' contains either 'AMD64' or 'x86' or other, if not AMD64 presume 32-bit

' ObjRegistry.GetStringValue?...
' http://msdn.microsoft.com/en-us/library/windows/desktop/aa390788%28v=vs.85%29.aspx

strPath = "SYSTEM\CurrentControlSet\Control\Session Manager\Environment"

ObjRegistry.GetSTRINGValue HKEY_LOCAL_MACHINE, strPath, "PROCESSOR_ARCHITECTURE", CPUarch

' CPUarch will be AMD64 or IA64 if 64-bit, otherwise 32-bit

' ********** Calculate values to be used **********

If CPUarch = "AMD64" or CPUarch = "IA64" Then
	AddCriticalWorkerThreads = TotalRAM * 3
	AddDelayedWorkerThreads = TotalRAM * 3
	DefaultWorkerThreads = 64
Else
	AddCriticalWorkerThreads = TotalRAM * 6
	AddDelayedWorkerThreads = TotalRAM * 6
	DefaultWorkerThreads = 64
end if

' WScript.echo "Total RAM: " & TotalRAM
' WScript.echo "Critical Worker Threads: " & AddCriticalWorkerThreads
' WScript.echo "Delayed Worker Threads: " & AddDelayedWorkerThreads
' WScript.echo "Default Worker Threads: " & DefaultWorkerThreads

' WScript.Quit

' ********** Set Additional Critical and Delayed Worker Threads ***********

strPath = "SYSTEM\CurrentControlSet\Control\Session Manager\Executive"

' Create key in case it doesn't exist yet
Return = objRegistry.CreateKey(HKEY_LOCAL_MACHINE, strPath)

ObjRegistry.SetDWORDValue HKEY_LOCAL_MACHINE, strPath, "AdditionalCriticalWorkerThreads", AddCriticalWorkerThreads
If Err <> 0 Then
	WScript.Echo "Could not set AdditionalCriticalWorkerThreads."
End If

ObjRegistry.SetDWORDValue HKEY_LOCAL_MACHINE, strPath, "AdditionalDelayedWorkerThreads", AddDelayedWorkerThreads
If Err <> 0 Then
	WScript.Echo "Could not set AdditionalDelayedWorkerThreads."
End If

' ********** Set Default Number of Worker Threads ***********

strPath = "SYSTEM\CurrentControlSet\Services\RpcXdr\Parameters"

' Create second key in case it doesn't exist yet
Return = objRegistry.CreateKey(HKEY_LOCAL_MACHINE, strPath)

ObjRegistry.SetDWORDValue HKEY_LOCAL_MACHINE, strPath, "DefaultNumberOfWorkerThreads", DefaultWorkerThreads
If Err <> 0 Then
	WScript.Echo "Could not set DefaultNumberOfWorkerThreads."
End If

' ********* End! **********

Set ObjRegistry = Nothing

' Wscript.echo "Done!"