In computing, a process is a running instance of a program, including all variables and other state. A multitaskingoperating system may just switch between processes to give the appearance of many processes executingconcurrently or simultaneously, though in fact only one process can be executing at any one time per CPUthread.
Some new processors, such as Athlon 64 X2 can actually execute two processes at a time, because they are multicore processors.
Intel's Pentium 4 with Hyperthreading capability have a different design: some doubled parts of the core allow the processor to make a context switch in almost no time.