Question

1. Can an operating system implement the two operational modes (user vs system) if the hardware does not support a mode bit? Explain.

2. Give an example of an operating system that does not implement the dual-mode protection.

3. Explain the main difference that exists between multiprogramming and multitasking.

Answer 1

1. There are two modes of operation in our systems these are user mode and Kernel mode. User mode and Kernel mode both are implemented by use of hardware . When computer system loads then hardware starts PC in kernel mode and firstly OS is loaded then OS changes the mode bit of hardware user mode. We can not implement two operational modes if the hardware does not support a mode bit because we switch our hardware to respective mode we want , it is a property that can be implemented only if our hardware supports mode bit. If there is no mode bit we can not swap from user to kernel mode and vice versa. So without mode bit we can not implement two operational modes of user and kernel.

2. In Intel 8088 which was a successor of 8086 , IBM developed DOS for it. SInce 8088 had no mode bit therefore DOS does not implement dual mode protection.

3. Multiprogramming is when many programs can be in ready queue and you are executing them using one cpu . So in multiprogramming many task such as word editor and browser both are in ready queue and your cpu is executing them . Now let 1,2,3,4 are processes in ready queue and 1 is going for execution after some time 1 needs some i/o operation so it goes for i/o during this time our cpu will execute task 2.

But in multitasking it does not matter whether task needs i/o operation or not , a time slice is allotted for each process and that process is executed that much amount of time in cpu then next program comes . multitasking is similar to multiprogramming . and there is no much difference. multiprogramming was done on old days and multitasking is just improvement on concept of multiprogramming so that each process can get a time so no process will be starved .