Question

3. In 1 paragraph for each

(a). What is a Virtual Machine and how does it differ from a physical machine?
(b). Describe the differences between multi-programming and multi-tasking?
(c). What is a context switch? (describe the mechanism, the reasons for a switch, and what is switched)

Answer 1

I have written only one paragraph as you asked, If you need more details with explanations, please let me know.

Virtual Machine vs Physical machine:

Physical machine has all functionalities like Desktop PC but it has more features like Multiple NICs and Redundant power supplies, large in size. Virtual machines are simulation of physical machine.
Physical machines are more expensive than VMs. Backing up physical machine due to failure is a nightmare. Scaling up physical machine is expensive. Since physical machines are dedicated, more powerful than VMs.
Every virtual machine has its own virtual hardware. So the guest operating system loaded on a VM is only aware of its hardware configuration and not the physical server’s. It means that the operation system installed on a VM is no longer tied up to certain hardware and you can easily move virtual machines from one physical server to another or even to another data center. The benefits of virtualization are obvious: Instead of having just one application per server, you can now run several guest Operating Systems and a handful of applications with the same physical hardware. With physcial servers, configuration should be done by our IT team. When there is a configuration problem, we may need to hire extra expert. But with VMs there are many best vendors outside who provides complete support. Even though VMs are cheaper, multi tasking, you are not the one who has control over VMs.

Multiprogramming vs Multitasking:

Let's say there are two programs currently active in the system. But our system can serve only one programa at a time. Program A has to wait for some IO operations. In the mean time, Systemc an serve programB. But it won't. It will waste simply CPU cycles. To avoid this, multiporgramming has been introduced. While program A is waiting for IO, program B can be served. So ultimate aim of multiprogramming is keeping CPU busy as much as possible.

Multiprogramming and multitasking are referring the same things. At any point cpu can execute only one programs while others are waiting for their turn. But there is a minor difference. Multiprogramming refers the whole applications whereas multitasking refers tasks. One application may have multiple tasks. Task can also refer to a thread of execution when one process is divided into sub tasks. Each smaller task does not hijack the CPU until it finishes like in the older multiprogramming but rather a fair share amount of the CPU time.

Context switch : what, why, how.

what: Switching from one task to another.
Reason for switch: When the current executing tasks has to wait for some IO operations, OS will do context-switch to maximize the utilization of CPU.
What is switched and the mechanism: Saves the register values of the current process. It explains the state of the current process. Load the newly selected process' register values. New process resumes from the place where it stops. It is possible because fo program counter.
Context switch can happen only in kernel mode.