Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
322756 How to back up and restore the registry in Windows
SecondLevelDataCache records the size of the processor cache, also known asthe secondary or L2 cache. If the value of this entry is 0, the systemattempts to retrieve the L2 cache size from the Hardware Abstraction Layer(HAL) for the platform. If it fails, it uses a default L2 cache size of 256KB. If the value of this entry is not 0, it uses this value as the L2 cachesize. This entry is designed as a secondary source of cache sizeinformation for computers on which the HAL cannot detect the L2 cache.
This is not related to the hardware; it is only useful for computers withdirect-mapped L2 caches. Pentium II and later processors do not have direct-mapped L2 caches. SecondLevelDataCache can increase performance byapproximately 2 percent in certain cases for older computers with amplememory (more than 64 MB) by scattering physical pages better in the addressspace so there are not so many L2 cache collisions. SettingSecondLevelDataCache to 256 KB rather than 2 MB (when the computer has a 2MB L2 cache) would probably have about a 0.4 percent performance penalty.