In multiprogrammed operating system, multiple ready to execute process stay in main memeory. Suppose main memory has four ready to execute jobs as J1, J2, J3, J4. Let's assume J4 is executing over CPU and after sometime, J4 needs some IO, so in this duration job J2 can take control of CPU for making CPU utilization more efficient. So in multiprogrammed system, CPU will multiplex over multiple jobs. This mechanism will led to scheduling concepts.This also a time sharing system where time sharing is not strict.
In multitasking system CPU will provide a share of time to a particilar job.Once time quantum is over the job will get preempted irrespective of the completion status of the job.