You probably mean processes... (threads a subdivisions of processes)...
As in fact no same-time is exists on a single processor core there is no logical limit to the number of process can be active in an operating system (may be a physical limit of memory to hold the table for processes).
Threads are subdivisions of a process and are managed under the process's thread pool. By default such thread pool can be hold about 500 threads but that number can be changed using the right API.
These thread pools are also limited only by the physical limits of memory...
So the process/thread number does not depends on the CPU model but on the OS (in Linux it handled differently)...
However the actual implementation of the execution of those processes/threads depending on the number of physical cores of the CPU - in Pentium 4 it can be 1 or 2 (using Hyper-Threading technology)...
About Processes and Threads[
^]
Intel Pentium 4[
^]
Submit an article or tip