if there is only one kind of active resource like CPU resou

if there is only one kind of active resource ( like CPU resources only), does multiprogramming still make sense? why?

Solution

The answer is YES.Because in a multiprogramming operating system there are one or more programs (processes or customers) resident in computer’s main memory ready to execute. Only one program at a time gets the CPU for execution while the others are waiting their turn. The whole idea of having a multi-programmed system is to optimize system utilization (more specifically CPU time). The currently executing program gets interrupted by the operating system between tasks (for example waiting for IO, recall the mail packaging example) and transfer control to another program in line (another customer). Running program keeps executing until it voluntarily gives the CPU back or when it blocks for IO. As we can see, the design goal is very clear: processes waiting for IO should not block other processes which in turn wastes CPU time. The idea is to keep the CPU busy as long as there are processes ready to execute.

In order for such a system to function properly, the operating system must be able to load multiple programs into separate partitions of the main memory and provide the required protection because the chance of one process being modified by another process is likely to happen. Other problems that need to be addressed when having multiple programs in memory is fragmentation as programs enter or leave (swapping) the main memory.

Another issue that needs to be handled as well is that large programs may not fit at once in memory which can be solved by using virtual memory. In modern operating systems programs are split into equally sized chunks called pages but this is beyond the scope of this article.

Multiprogramming operating system allows multiple processes to reside in main memory where only one program is running. The running program keeps executing until it blocks for IO and the next program in line takes the turn for execution. The goal is to optimize CPU utilization by reducing CPU idle time. Finally, please note that the term multi-programming is an old term because in modern operating systems the whole program is not loaded completely into the main memory.

In multi programming though the CPU is shared between programs it is not the perfect example on CPU time sharing because one program keeps running until it blocks however in a multitasking (modern operating system)
time sharing is best manifested because each running process takes only a fair amount of the CPU time called quantum time.