Question

1. describe, in step-by-step form, the procedure that the operating system would use to switch from one user to another in a multiuser time sharing system.
2. Discuss the steps that take place when a process is moved a) from ready state to running state; b) from running state to blocked state; c) from running state to ready state, and d) from blocked state to ready state.
3. Explain deadlocking.
4. The CPU scheduling algorithm (in UNIX) is a simple priority algorithm. The priority for a process is computed as the ratio of the CPU time actually used by the process to the real time that has passed. The lower the figure, the higher the priority. Priorities are recalculated every 10^th of a second.

1. What kind of jobs are favoured by this type of algorithm?
2. If there is no I/O being performed, this algorithm reduces to a round-robin algorithm. Explain.
3. Discuss this algorithm in terms of the scheduling objectives give in the reference text.

5. Explain the bootstrap procedure for a diskless workstation.

Answer 1

a) from ready to running-

  The process is waiting to be assigned to a processor. Ready processes are waiting to have the processor allocated to them by the operating system so that they can run.
Once the process has been assigned to a processor by the OS scheduler, the process state is set to running and the processor executes its instructions.

b)from running to blocked state-

process moves into the waiting state if it needs to wait for a resource, such as waiting for user input, or waiting for a file to become available.

c)running state to ready state:

Process may come into ready state from running state for interrupted by the scheduler to assign CPU to some other process.

d) from blocked state to ready state:

the process in the blocked state waiting for the resource which is not available and after the process gets the resourse for which is waiting for then it go back to the ready state and waiting for the processor to assign it.

deadlock

A process in operating systems uses different resources and uses resources in such way that,
1) Requests a resource
2) Use the resource
3) Releases the resource

Deadlock is a situation where a set of processes are blocked because each process is holding a resource and waiting for another resource acquired by some other process.
Consider an example when two buses are coming toward each other on same track and there is only one track, none of the buses can move once they are in front of each other. Similar situation occurs in operating systems when there are two or more processes hold some resources and wait for resources held by others.

Deadlock can arise if four conditions hold :
Mutual Exclusion: One or more than one resource are non-sharable (Only one process can use at a time)
Hold and Wait: A process is holding at least one resource and waiting for resources.
No Preemption: A resource cannot be taken from a process unless the process releases the resource.
Circular Wait: A set of processes are waiting for each other in circular form.

Less cpu bound and more i/o bound jobs are favoured in this type of algorithm.

since there is no i/o bound jobs so only cpu bound jobs ,and priorities are re-calculated every 10 second as it say in the above. so it drastically involve the flavour of round-robin algorithm.

functions of bootstrap:

bootstrap request is broadcast

bootstrap requires only a single packet exchange

bootstrap uses UDP-> Bootstrapping can occur across a router

bootstrap UDP to use checksum

bootstrap replies are also broadcast (since no one knows the requesters IP address, ARP will fail).

bootstrap requests and replies are sent with "no fragment bit" set.

Multiple replies -> process the first one

Clients uses timeout and retransmission

The timeout interval is random to avoid synchronization after a power failure