ACUCOBOL-GT implements multithreading in a machine-independent fashion. It neither needs nor uses any multithreading capabilities of the host system. This has several advantages:
There are, however, a few disadvantages to this implementation. Chief among these is that the operating system is not aware that there are multiple threads running in the runtime's process. This is primarily an issue on systems that have multiple processors. Some of these systems can allocate additional processors to a task if they know that the task contains more than one thread - up to one processor per thread. But because these systems do not see the runtime as a multithreaded entity, multiprocessor allocation does not happen.
Typically, multiprocessor systems are used to provide support for more users. By having more processors in the system, the system can run more processes at once, and in this way increase the number of users the machine can effectively support. But the system will not increase performance for a single process (assuming that the process gets 100% of the CPU's time - an unrealistic assumption in a production environment). In practice, a multiprocessor machine will usually not benchmark any better than a single processor machine for single-task benchmarks, but they will provide much better total throughput in a multi-user production environment.
In summary, multithreading an ACUCOBOL-GT program will not affect its performance in any special way on a multiprocessor machine. Any gain, or loss, will be the same as for a single processor system.