Question

Subject: Operating System.

I need a quick response, please kindly reply with a text/message not pictures.

Q1. What are the kernel threads? How does the affect the scheduling in one-to-one, one-to-many, and many-to-many systems?

Q2. Describe in detail the different types of OS structures. Which OS structure is most robust and why?

Please kindly solve the above two questions as soon as possible like in an hour, please.

Answer 1

1. Kernel threads:

It is an entity that can be scheduled. It is managed by a scheduler in the system. It represents a task running in kernel mode. Hence, it is an entity in kernel space and can include processes or handlers for interrupts. One thread can reference another thread. It can also run inside another process.

Kernel threads in one-to-one, one-to-many, and many-to-many systems:

• In one-to-one system, kernel thread is used to manage different user threads. It is used to overcome various problems. Such as system call blocking or process split across many processors.
• In one to many systems, one user thread can relate to many kernel threads. Blocking one kernel level thread doesn't block the process because of the availability of other many user threads.
• In many to many systems, many user threads are used. It is done by sharing the best features of the other two systems. Users are allowed to create as many threads as possible.

2. Types of OS structures:

Normal structure:

In this type, there is no well defined criteria. This is used with small systems. The interface and functions of the OS might not be separated properly. An example here is of MS DOS.

Layers:

In layered structure, the entire system is broken into chunks or layers. Every layer represents a level in the OS. There is an interface between two layers to facilitate communication between them. It simplifies the structure and functionality in the OS.

Micro kernel:

In this all the non necessary parts are removed from the kernel and are implemented as user or system level programs. In this way, a small or micro kernel is formed. It is the best structure since one can easily modify the user space services and the kernel will not get affected.

Modular structure:

In this structure, there are different modules in the OS. These modules are usually dynamically loadable. This also means that the kernel will have only some parts of core functionality. It is somewhat similar to layered structure. But it is more flexible than that.

Robust structure:

The most robust structure is said to be micro-kernel. This is because the kernel doesn't require any modification or update if there is any user service addition. Also it is more reliable and secure in that way. If there is any service failure, the rest of the OS will still function well.