A memory page containing a heavily used variable that was initialized very early and is in constant use is removed when

Consider the following heap (figure) in which blank regions are not in use and hatched region are in use.

The sequence of requests for blocks of size 300, 25, 125, 50 can be satisfied if we use

Consider the resource allocation graph given in the figure.

(a) Find if the system is in a deadlock state. (b) Otherwise, find a safe sequence.

Consider allocation of memory to a new process. Assume that none of the existing holes in the memory will exactly fit the process’s memory requirement. Hence, a new hole of smaller size will be created if allocation is made in any of the existing holes. Which one of the following statements is TRUE?

Consider the following statements about process state transitions for a system using preemptive scheduling.

I. A running process can move to ready state.
II. A ready process can move to running state.
III. A blocked process can move to running state.
IV. A blocked process can move to ready state.

Which of the above statements are TRUE?

Consider the following set of processes, assumed to have arrived at time 0. Consider the CPU scheduling algorithms Shortest Job First (SJF) and Round Robin (RR). For RR, assume that the processes are scheduled in the order P₁,P₂,P₃,P₄.

If the time quantum for RR is 4 ms, then the absolute value of the difference between the average turnaround times (in ms) of SJF and RR (round off to 2 decimal places) is _____.

Each of a set of n processes executes the following code using two semaphores a and b initialized to 1 and 0, respectively. Assume that count is a shared variable initialized to 0 and not used in CODE SECTION P.

wait (a); count = count+1;
if (count==n) signal (b);
signal (a); wait (b); signal (b);

What does the code achieve?

Consider the following five disk access requests of the form (request id, cylinder number) that are present in the disk scheduler queue at a given time.

         (P, 155), (Q, 85), (R, 110), (S, 30), (T, 115) 

Assume the head is positioned at cylinder 100. The scheduler follows Shortest Seek Time First scheduling to service the requests.

Which one of the following statements is FALSE?

Consider a paging system that uses a 1-level page table residing in main memory and a TLB for address translation. Each main memory access takes 100 ns and TLB lookup takes 20 ns. Each page transfer to/from the disk takes 5000 ns. Assume that the TLB hit ratio is 95%, page fault rate is 10%. Assume that for 20% of the total page faults, a dirty page has to be written back to disk before the required page is read in from disk. TLB update time is negligible. The average memory access time in ns (round off to 1 decimal places) is ______.

The process state transition diagram in below figure is representative of

A critical section is a program segment

Which of the following is an example of spooled device?

The correct matching for the following pairs is

         A. Activation record	   1. Linking loader
         B. Location counter	   2. Garbage collection
         C. Reference counts	   3. Subroutine call
         D. Address relocation	   4. Assembler 

A 1000 Kbyte memory is managed using variable partitions but to compaction. It currently has two partitions of sizes 200 Kbytes and 260 Kbytes respectively. The smallest allocation request in Kbytes that could be denied is for

A solution to the Dining Philosophers Problem which avoids deadlock is

Four jobs to be executed on a single processor system arrive at time 0⁺ in the order A, B, C, D. their burst CPU time requirements are 4, 1, 8, 1 time units respectively. The completion time of A under round robin scheduling with time slice of one time unit is

A demand paged virtual memory system uses 16 bit virtual address, page size of 256 bytes, and has 1 Kbyte of main memory. LRU page replacement is implemented using a list whose current status (page number in decimal) is

For each hexadecimal address in the address sequence given below

 00FF, 010D, 10FF, 11B0

indicate
(i) the new status of the list
(ii) page faults, if any, and
(iii) page replacements, if any

The concurrent programming constructs fork and join are as below:
fork which creates a new process executing from the specified label
join which decrements the specified synchronization variable (by 1) and terminates the process if the new value is not 0.
Show the precedence graph for S1, S2, S3, S4, and S5 of the concurrent program below.

   N = 2
   M = 2
   fork L3
   fork L4
   S1
L1:join N
   S3
L2:join M
   S5
L3:S2
   goto L1
L4:S4
   goto L2
next: 

A computer system uses the Banker’s Algorithm to deal with deadlocks. Its current state is shown in the table below, where P0, P1, P2 are processes, and R0, R1, R2 are resources types.

(a) Show that the system can be in this state.
(b) What will the system do on a request by process P0 for one unit of resource type R1?

A file system with a one-level directory structure is implemented on a disk with disk block size of 4K bytes. The disk is used as follows:

 Disk-block 0: File Allocation Table, consisting of one 8-bit entry per date block, 
               representing the data block address of the next date block in the file
 Disk block 1: Directory, with one 32 bit entry per file:
 Disk block 2: Data block 1;
 Disk block 3: Data block 2; etc. 

(a) What is the maximum possible number of files?
(b) What is the maximum possible file size in blocks?

Locality of reference implies that the page reference being made by a process

The correct matching for the following pairs is

(A) Disk Scheduling        (1) Round robin
(B) Batch Processing       (2) SCAN
(C) Time sharing           (3) LIFO
(D) Interrupt processing   (4) FIFO  

I/O redirection

Thrashing

Dirty bit for a page in a page table

An operating system contains 3 user processes each requiring 2 units of resource R. The minimum number of units of r such that no deadlocks will ever arise is

Each Process P_i, i = 1.......9 is coded as follows

    repeat 
           P(mutex)
           {Critical section}
           V(mutex)
    forever   

The code for P₁₀ is identical except it uses V(mutex) in place of P(mutex). What is the largest number of processes that can be inside the critical section at any moment?

Threads of a process share

Consider the following CPU processes with arrival times (in milliseconds) and length of CPU bursts (in milliseconds) as given below:

If the pre-emptive shortest remaining time first scheduling algorithm is used to schedule the processes, then the average waiting time across all processes is __________ milliseconds.

A multithreaded program P executes with x number of threads and used y number of locks for ensuring mutual exclusion while operating on shared memory locations. All locks in the program are non-reentrant, i.e., if a thread holds a lock l, then it cannot re-acquire lock l without releasing it. If a thread is unable to acquire a lock, it blocks until the lock becomes available. The minimum value of x and the minimum value of y together for which execution of P can result in a deadlock are:

A linker reads four modules whose lengths are 200, 800, 600 and 500 words, respectively. If they are loaded in that order, what are the relocation constants?

Which of the following is an example of a spooled device?

When  the  result  of  a  computation  depends  on  the  speed  of  the  processes involved there is said to be

A counting semaphore was initialized to 10. Then 6P (wait) operations and 4V (signal) operations were completed on this semaphore. The resulting value of the semaphore is

A  computer  has  six  tape  drives,  with  n  processes  competing  for  them.  Each process may need two drives. What is the maximum value of n for the system to be deadlock free?

The overlay tree for a program is as shown below:

What will be the size of the partition (in physical memory) required to load (and run) this program?

Consider n processes sharing the CPU in a round-robin fashion. Assuming that each process switch takes s seconds, what must be the quantum size q such that the overhead resulting from process switching is minimized but at the same time each process is guaranteed to get its turn at the CPU at least every t seconds?

If an instruction takes i microseconds and a page fault takes an additional j microseconds, the effective instruction time if on the average a page fault occurs every k instruction is:

(a) Free disk space can be kept track of using a free list or a bit map. Disk addresses require d bits. For a disk with 13 blocks, F of which is free, state the condition under which the free list uses less space than the bit map.

(b) Consider a disk with C cylinders, t tracks per cylinder, s sectors per track and a sector length sl. A logical file dl with fixed record length rl is stored continuously on this disk starting at location (c_L,t_L,s_L), where c_L, t_L and S_L are the cylinder, track and sector numbers, respectively. Derive the formula to calculate the disk address (i.e. cylinder, track and sector) of a logical record n assuming that rl=sl.

Listed below are some operating system abstractions (in the left column) and the hardware components or mechanism (in the right column) that they are abstractions of. Which of the following matching of pairs is correct?

    A. Thread                      1. Interrupt
    B. Virtual address space       2. Memory
    C. File system                 3. CPU
    D. Signal                      4. Disk 

Which of the following disk scheduling strategies is likely to give the best through put?

System calls are usually invoked by using

A  multi-user,  multi-processing  operating  system  cannot  be  implemented  on hardware that does not support

Which of the following is/are advantage of virtual memory?