If you have ever run NET CONFIG SERVER in conjunction with the /AUTODISCONNECT, /SERVCOMMENT OR /HIDDEN switches, you have accidentally turned off Windows NT auto-tuning of the SERVER service. This also disables the effect of tuning in Control Panel / Network / Server / Properties. If you add or remove RAM, appropriate tuning of the SERVER service does not happen.

To restore auto-tuning, edit:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters

and remove all the extries except the following, and ones that specifically set:

EnableSharedNetDrives
Lmannounce
NullSessionPipes
NullSessionShares
Size
Tune the SERVER service using tip 7268 ยป TuneSVR.bat tunes the Server service in batch.