I am about to install DIRAC on a 64-bit machine, should I compile using 64-bit integers or 32-bit integers?¶
DIRAC runs smoothly (with few exceptions; see below) on 64-bit platforms using either 32-bit or 64-bit integers.
It is easier to install for 32-bit integers because MPI and math libraries are typically built for 32-bit integers. Therefore DIRAC is by default built for 32-bit integers.
If you decide to build for 32-bit integers, you will not be able to:
Safely allocate more than 16 GB of memory per cpu-core
Run really, really large Coupled-Cluster calculations
If you want to be able to run the above calculations, you have to build for 64-bit integers.
If you decide to build for 64-bit integers, you have to make sure that the math library you link to can handle 64-bit integers.
Otherwise DIRAC will stop.