i already configured AWE enable and max server memory to 24 GB, i dont think its in effect because it shows in task manager only 3.5 GB consume.
Because locked pages is not enabled. Or because Task Manager is reporting memory usage incorrectly as it usually does.
Don't add SQL to the administrators group, that's against security best practices. Add the sql server service account to the list of accounts that have lock pages in memory permission. If you can't do it, ask your AD administrator to do it for you.
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: Discussions on DB performance with occasional diversions into recoverability
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