Hi Talla,
The difference between 57 GB and 64 GB is only 6 GB. Windows OS is going to consume 4 GB, then you have other programs open, like Workbench. There is only a 2 GB margin left, and the in-core memory estimate is approximate.
Sometimes, even if you have a bigger margin, if you have been using the computer for a while, the memory can get fragmented and there is no single block of free memory as large as it needs to allocate, so it uses out-of-core. This can be remedied by restarting the computer and trying again.
There is a command snippet to force the solver to try in-core. If you are using Distributed solver it is:
DSPOPTION,,INCORE
Note the two commas, that is not a typo. That will force the solver to start incore. However, if it is a multistep solve, it may switch to out-of-core at a later step if it needs more memory than is available.
You are navigating away from the AIS Discovery experience