WinNT 4.0 PIII 550 2M Cache

Yes its true.

HKLM\System\CurrentControlSet\control\sessionmanager\memory management
**One path wrapped

The value is SecondLevelDataCache
default is 0 modify to the amount of L2 in K
(ie 2M is 2048)

MS KB Q183063

However, it should have little if any effect on PII or higher processors

Hope this helps.
Howie

Found this on TechNet under Registry Tweaks:
Sounds like you should be very careful when doing this...

Getting the Most from Your Cache

By default, the NT HAL tries to recognize the amount of L2 cache on your motherboard. Sometimes it succeeds, and sometimes it fails. You can make sure that the HAL knows how much cache you have installed by checking the value of the SecondLevelDataCache REG_DWORD value under the HKLM\System\CurrentControlSet\Control\Session Manager\Memory Management key.
When this value is 0, that tells the HAL that you have 256Kb of L2 cache. If you have a different amount installed, set SecondLevelDataCache to the amount, in Kb, of cache you've actually got. For example, if you have a 512Kb cache, set the value to be a decimal value of 512 or a hex value of 0x200. If you get this wrong, your machine may be unstable, so make sure to enter the right value in the right base.