Operating Systems

1. Explain the concept of Reentrancy?
   It is a useful, memory-saving technique for multiprogrammed timesharing systems. A Reentrant Procedure is one in which multiple users can share a single copy of a program during the same period. Reentrancy has 2 key aspects: The program code cannot modify itself, and the local data for each user process must be stored separately. Thus, the permanent part is the code, and the temporary part is the pointer back to the calling program and local variables used by that program. Each execution instance is called activation. It executes the code in the permanent part, but has its own copy of local variables/parameters. The temporary part associated with each activation is the activation record. Generally, the activation record is kept on the stack.

   Note: A reentrant procedure can be interrupted and called by an interrupting program, and still execute correctly on returning to the procedure.
2. Explain Belady's Anomaly?
   Also called FIFO anomaly. Usually, on increasing the number of frames allocated to a process virtual memory, the process execution is faster, because fewer page faults occur. Sometimes, the reverse happens, i.e., the execution time increases even when more frames are allocated to the process. This is Belady's Anomaly. This is true for certain page reference patterns.
3. What is a binary semaphore? What is its use?
   A binary semaphore is one, which takes only 0 and 1 as values. They are used to implement mutual exclusion and synchronize concurrent processes.

UNIX File Management

1. How are devices represented in UNIX?
   All devices are represented by files called special files that are located in /dev directory. Thus, device files and other files are named and accessed in the same way. A 'regular file' is just an ordinary data file in the disk. A 'block special file' represents a device with characteristics similar to a disk (data transfer in terms of blocks). A 'character special file' represents a device with characteristics similar to a keyboard (data transfer is by stream of bits in sequential order).
2. What is 'inode'?
   All UNIX files have its description stored in a structure called 'inode'. The inode contains info about the file-size, its location, time of last access, time of last modification, permission and so on. Directories are also represented as files and have an associated inode. In addition to descriptions about the file, the inode contains pointers to the data blocks of the file. If the file is large, inode has indirect pointer to a block of pointers to additional data blocks (this further aggregates for larger files). A block is typically 8k.

   
   

   Inode consists of the following fields:

   
   

   1. File owner identifier
   2. File type
   3. File access permissions
   4. File access times
   5. Number of links
   6. File size
   7. Location of the file data
3. Brief about the directory representation in UNIX.
   A Unix directory is a file containing a correspondence between filenames and inodes. A directory is a special file that the kernel maintains. Only kernel modifies directories, but processes can read directories. The contents of a directory are a list of filename and inode number pairs. When new directories are created, kernel makes two entries named '.' (refers to the directory itself) and '..' (refers to parent directory). System call for creating directory is mkdir (pathname, mode).
   

Arithmetic Reasoning

1.The total of the ages of Amar, Akbar and Anthony is 80 years. What was the total of their ages three years ago ?

71 years 72 years 74 years 77 years

2. Two bus tickets from city A to B and three tickets from city A to C cost Rs. 77 but three tickets from city A to B and two tickets from city A to C cost Rs. 73. What are the fares for cities B and C from A ?

Rs. 4, Rs. 23 Rs. 13, Rs. 17 Rs. 15, Rs. 14 Rs. 17, Rs. 13

3.An institute organised a fete and 1/5 of the girls and 1/8 of the boys participated in the same. What fraction of the total number of students took part in the fete ?

2/13 13/40 Data inadequate None of these

4.A number of friends decided to go on a picnic and planned to spend Rs. 96 on eatables. Four of them, however, did not turn up. As a consequence, the remaining ones had to contribute Rs. 4 each extra. The number of those who attended the picnic was

8 12 16 24

5.A, B, C, D and E play a game of cards. A says to B, "If you give me three cards, you will have as many as E has and if I give you three cards, you will have as many as D has." A and B together have 10 cards more than what D and E together have. If B has two cards more than what C has and the total number of cards be 133, how many cards does B have ?

22 23 25 35

Verification of Truth

1. A train always has

Rails Driver Guard Engine

2.Which one of the following is always found in 'Bravery'?

Experience Power Courage Knowledge

3.A song always has

Word Chorus Musician Tymbal

4.Yesterday I saw an ice cube which had already melted due to heat of a nearby furnace.

Always Never Often Sometimes

5.What is found necessarily in milk?

Cream Curd Water Whiteness

Classification

1.Choose the word which is different from the rest.

Chicken Snake Swan Crocodile

2.Choose the word which is different from the rest.

Cap Turban Helmet Veil

3.Choose the word which is different from the rest.

Kiwi Eagle Emu Ostrich

4.Choose the word which is different from the rest.

Rigveda Yajurveda Atharvaveda Ayurveda

5.Choose the word which is different from the rest.

Curd Butter Oil Cheese

Direction Sense Test

1. One morning Udai and Vishal were talking to each other face to face at a crossing. If Vishal's shadow was exactly to the left of Udai, which direction was Udai facing?

East West North South

2.Y is in the East of X which is in the North of Z. If P is in the South of Z, then in which direction of Y, is P?

North South South-East None of these

3. If South-East becomes North, North-East becomes West and so on. What will West become?

North-East North-West South-East South-West

4.A man walks 5 km toward south and then turns to the right. After walking 3 km he turns to the left and walks 5 km. Now in which direction is he from the starting place?

West South North-East South-West

5.Rahul put his timepiece on the table in such a way that at 6 P.M. hour hand points to North. In which direction the minute hand will point at 9.15 P.M. ?

South-East South North West

Analogy

1.CUP : LIP :: BIRD : ?

BUSH GRASS FOREST BEAK

2.Flow : River :: Stagnant : ?

Rain Stream Pool Canal

3.Ornithologist : Bird :: Archealogist : ?

Islands Mediators Archealogy Aquatic

4.Peacock : India :: Bear : ?

Australia America Russia England

5. REASON : SFBTPO :: THINK : ?

SGHMJ UIJOL UHNKI UJKPM

Cube and Cuboid

1.How many cubes having red, green and black colours on at least one side of the cube will be formed ?

16 12 10 4

2.How many small cubes will be formed ?

6 12 16 24

3.How many cubes will have 4 coloured sides and two non-coloured sides ?

8 4 16 10

4.How many cubes will have green colour on two sides and rest of the four sides having no colour ?

12 10 8 4

5.How many cubes will remain if the cubes having black and green coloured are removed ?

4 8 12 16

Seating Arrangement

1.A, P, R, X, S and Z are sitting in a row. S and Z are in the centre. A and P are at the ends. R is sitting to the left of A. Who is to the right of P ?

A X S Z

2.A, B, C, D and E are sitting on a bench. A is sitting next to B, C is sitting next to D, D is not sitting with E who is on the left end of the bench. C is on the second position from the right. A is to the right of B and E. A and C are sitting together. In which position A is sitting ?

Between B and D Between B and C Between E and D Between C and E

3. In a class there are seven students (including boys and girls) A, B, C, D, E, F and G. They sit on three benches I, II and III. Such that at least two students on each bench and at least one girl on each bench. C who is a girl student, does not sit with A, E and D. F the boy student sits with only B. A sits on the bench I with his best friends. G sits on the bench III. E is the brother of C.How many girls are there out of these 7 students ?

3 3 or 4 4 Data inadequate

4.Which of the following is the group of girls ?

BAC BFC BCD CDF

5.Who sits with C ?

B D G E