Many systems have an external or secondary cache that is configured to handle a certain amount of memory in the system. If this is wrongly configured or too small it could cause the system to suffer from cache overload. This is where the cache memory attempts to handle the requests for the larger memory but due to lack of space can cause as much of a burden as having no cache at all. The number of cache hits will go down and the CPU will be left waiting for the main (slower) memory to provide the data. The answer is to add/configure the cache to work with the extra main memory. For details and to see if this is required for your system check your Hardware OEM specifications for details of the external/secondary cache size and required settings.