User level threads are threads that are visible to the programmer and are unknown to the kernel. The operating system kernel supports and manages kernel level threads. Three different types of models relate user and kernel level threads.

Which of the following statements is/are true ?

(a)

(i) The Many - to - one model maps many user threads to one kernel thread

(ii) The one - to - one model maps one user thread to one kernel thread

(iii) The many - to - many model maps many user threads to smaller or equal kernel threads

(b)

(i) Many - to - one model maps many kernel threads to one user thread

(ii) One - to - one model maps one kernel thread to one user thread

(iii) Many - to- many model maps many kernel threads to smaller or equal user threads

The correct answer is option 1.

CONCEPT:

• Threads are lightweight processes because they have their own stack but can access shared data. Because threads share the same address space as the process and other threads within the process, the operational cost of communication between the threads is low, which is an advantage. 

• The many–to–one model maps many user threads to one kernel thread.
• The one–to–one model maps one user thread to one kernel thread.
• The many–to–many model maps many user threads to smaller or equal kernel threads.

EXPLANATION

​

∴ Hence the correct answer is (a) is true; (b) is false.

Additional Information

Multiple threads of the same process share other resources of the process except for register, stack, and stack pointer. In particular, a process is generally considered to consist of a set of threads sharing an address space, heap, static data, code segments, and file descriptors.

Thread of the same process doesn't share program counter (register), stack,  registers