what determines the amount of threads you can use

what determines the amount of threads you can use ? (in order to get more done in the same amount of time)

the reason im asking is because i have seen some posts say they would need minimum 16GB of ram,
but also that GSA SER is 32 bit & that anything over 3GB of ram would not make any difference.

ive taken account of various things to try & make it more efficient etc. & keeping an eye of
memory & cpu usage at bottom of GSA SER interface.

i have 4gb of ram, so would getting more ram make any difference ?