多线程可以在单处理器系统上实现吗？

I have always followed the concept that multithreading can only be implemented on multiple processors system where there are more than one processor to be assigned to each thread and each thread can be executed simultaneoulsy. There is no scheduling in this case as each of the thread has separate resources all dedicated to it. But I recenetly read it somewhere that I can do multithreading on single processor system as well. Is it correct? and if yes then what is the difference between single processor and multiple processor systems?I have always followed the concept that multith