Hardware/CPU cores can limit the number of threads you can assign to Parallel backup jobs.
On a single CPU / 8-Core system means that this system can handle 16 threads but will not handle 32 threads.
Also when you are using Parallel backups(pwalk) can cause threads to hang and will not release it.
Details of hows cores effect thread operations.
A core is a single computing component with independent CPU. A core is defined as a CPU which read and execute program instructions. Number of cores directly affect processing speed of Device. The more number of cores you have the faster Processing you get.
It simply means number of CPUs you have to run a single Device. A multi-core processor is a single computing component with two or more independent processing units called cores. (Dual Core , Quad Core , Octa core and now you have Hexa core also.) They have shared Secondary memory, private cache memory and separate Registers.
Process Thread :-
It is just a portion of a Process that CPU currently executing. Larger programs are divided into threads (small sections) so that processor can execute them simultaneously to get fast execution.
Hyper Threading :-
Example - It means that the CPU has 2 physical cores but can process 4 threads simultaneously through hyper threading.
In reality, one physical core can only truly run one thread at a time, but using hyper threading, the CPU exploits the idle stages in the pipeline to process another thread.