When does the minimum server memory setting take effect?
There is a popular believe that when the SQL Server engine starts it will consume this mount of memory. Not true!
On start up SQL Server will use whatever memory is required. This may not meet the minimum memory setting. Once the database load reaches or exceeds the minimum server memory setting, SQL Server keep the minimum server memory and not release it back to the operating system.
In the case above, the memory is set to 512MB. However, SQL Server used less than that on start up.
Read more about this under the “Setting the memory options manually”” section in this TechNet article: http://technet.microsoft.com/en-us/library/ms178067.aspx