Max memory means maximum memory that can be used, not memory that is actually being used. So just because max memory is set to 100GB, doesn't mean you're using 100GB. You've also used the terms "target" and "total" memory - what do they mean and where do you get the numbers from?

This is my last attempt to get a comprehensible answer. SQL Server is using 24GB. You have 4GB free. That's 28GB accounted for. What's using the other 100GB? Feel free to help us by including results from sp_configure, screen shots, or anything else that may assist our understanding of where your numbers come from.

John