Look for SQL Server:Memory Manager (as MSSQL$InstanceName:Memory Manager) counters:

- Target Server Memory (KB) is how much memory the instance would want to use if the demand was there from active processes and the memory were available.

- Total Server Memory (KB) is how much memory the instance actually is using at the moment.

Once the buffer pool is warmed up those numbers will generally be the same, but immediately after a restart, or if demand for data never reaches the capabilities of the server memory, Target will be lower than Total.

See Page 153 of Troubleshooting SQL Server: A Guide for the Accidental DBA[/url] for more info.