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Technical Operating Systems

Technical 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.

4.What is thrashing?
It is a phenomenon in virtual memory schemes when the processor spends most of its time swapping pages, rather than executing instructions. This is due to an inordinate number of page faults.

5.List the Coffman's conditions that lead to a deadlock.
Mutual Exclusion: Only one process may use a critical resource at a time.
Hold & Wait: A process may be allocated some resources while waiting for others.
No Pre-emption: No resource can be forcible removed from a process holding it.
Circular Wait: A closed chain of processes exist such that each process holds at least one resource needed by another process in the chain.


6.What are short-, long- and medium-term scheduling?
Long term scheduler determines which programs are admitted to the system for processing. It controls the degree of multiprogramming. Once admitted, a job becomes a process.
Medium term scheduling is part of the swapping function. This relates to processes that are in a blocked or suspended state. They are swapped out of real-memory until they are ready to execute. The swapping-in decision is based on memory-management criteria.
Short term scheduler, also know as a dispatcher executes most frequently, and makes the finest-grained decision of which process should execute next. This scheduler is invoked whenever an event occurs. It may lead to interruption of one process by preemption.

7.What are turnaround time and response time?
Turnaround time is the interval between the submission of a job and its completion. Response time is the interval between submission of a request, and the first response to that request.

8.What are the typical elements of a process image?
User data: Modifiable part of user space. May include program data, user stack area, and programs that may be modified.
User program: The instructions to be executed.
System Stack: Each process has one or more LIFO stacks associated with it. Used to store parameters and calling addresses for procedure and system calls.
Process control Block (PCB): Info needed by the OS to control processes.

9.What is the Translation Lookaside Buffer (TLB)?
In a cached system, the base addresses of the last few referenced pages is maintained in registers called the TLB that aids in faster lookup. TLB contains those page-table entries that have been most recently used. Normally, each virtual memory reference causes 2 physical memory accesses-- one to fetch appropriate page-table entry, and one to fetch the desired data. Using TLB in-between, this is reduced to just one physical memory access in cases of TLB-hit.

10.What is the resident set and working set of a process?
Resident set is that portion of the process image that is actually in real-memory at a particular instant. Working set is that subset of resident set that is actually needed for execution. (Relate this to the variable-window size method for swapping techniques.)
Technical Operating Systems

11.When is a system in safe state?
The set of dispatchable processes is in a safe state if there exists at least one temporal order in which all processes can be run to completion without resulting in a deadlock.

12.What is cycle stealing?
We encounter cycle stealing in the context of Direct Memory Access (DMA). Either the DMA controller can use the data bus when the CPU does not need it, or it may force the CPU to temporarily suspend operation. The latter technique is called cycle stealing. Note that cycle stealing can be done only at specific break points in an instruction cycle.

13.What is meant by arm-stickiness?
If one or a few processes have a high access rate to data on one track of a storage disk, then they may monopolize the device by repeated requests to that track. This generally happens with most common device scheduling algorithms (LIFO, SSTF, C-SCAN, etc). High-density multisurface disks are more likely to be affected by this than low density ones.

14.What are the stipulations of C2 level security?
C2 level security provides for:
Discretionary Access Control
Identification and Authentication
Auditing
Resource reuse

15.What is busy waiting?
The repeated execution of a loop of code while waiting for an event to occur is called busy-waiting. The CPU is not engaged in any real productive activity during this period, and the process does not progress toward completion.

16.Explain the popular multiprocessor thread-scheduling strategies.
Load Sharing: Processes are not assigned to a particular processor. A global queue of threads is maintained. Each processor, when idle, selects a thread from this queue. Note that load balancing refers to a scheme where work is allocated to processors on a more permanent basis.
Gang Scheduling: A set of related threads is scheduled to run on a set of processors at the same time, on a 1-to-1 basis. Closely related threads / processes may be scheduled this way to reduce synchronization blocking, and minimize process switching. Group scheduling predated this strategy.
Dedicated processor assignment: Provides implicit scheduling defined by assignment of threads to processors. For the duration of program execution, each program is allocated a set of processors equal in number to the number of threads in the program. Processors are chosen from the available pool.
Dynamic scheduling: The number of thread in a program can be altered during the course of execution.

17.When does the condition 'rendezvous' arise?
In message passing, it is the condition in which, both, the sender and receiver are blocked until the message is delivered.

18.What is a trap and trapdoor?
Trapdoor is a secret undocumented entry point into a program used to grant access without normal methods of access authentication. A trap is a software interrupt, usually the result of an error condition.

19.What are local and global page replacements?
Local replacement means that an incoming page is brought in only to the relevant process' address space. Global replacement policy allows any page frame from any process to be replaced. The latter is applicable to variable partitions model only.

20.Define latency, transfer and seek time with respect to disk I/O.
Seek time is the time required to move the disk arm to the required track. Rotational delay or latency is the time it takes for the beginning of the required sector to reach the head. Sum of seek time (if any) and latency is the access time. Time taken to actually transfer a span of data is transfer time.
Technical Operating Systems

21.Describe the Buddy system of memory allocation.
Free memory is maintained in linked lists, each of equal sized blocks. Any such block is of size 2^k. When some memory is required by a process, the block size of next higher order is chosen, and broken into two. Note that the two such pieces differ in address only in their kth bit. Such pieces are called buddies. When any used block is freed, the OS checks to see if its buddy is also free. If so, it is rejoined, and put into the original free-block linked-list.

22.What is time-stamping?
It is a technique proposed by Lamport, used to order events in a distributed system without the use of clocks. This scheme is intended to order events consisting of the transmission of messages. Each system 'i' in the network maintains a counter Ci. Every time a system transmits a message, it increments its counter by 1 and attaches the time-stamp Ti to the message. When a message is received, the receiving system 'j' sets its counter Cj to 1 more than the maximum of its current value and the incoming time-stamp Ti. At each site, the ordering of messages is determined by the following rules: For messages x from site i and y from site j, x precedes y if one of the following conditions holds....(a) if Ti
23.How are the wait/signal operations for monitor different from those for semaphores?
If a process in a monitor signal and no task is waiting on the condition variable, the signal is lost. So this allows easier program design. Whereas in semaphores, every operation affects the value of the semaphore, so the wait and signal operations should be perfectly balanced in the program.


24.In the context of memory management, what are placement and replacement algorithms?
Placement algorithms determine where in available real-memory to load a program. Common methods are first-fit, next-fit, best-fit. Replacement algorithms are used when memory is full, and one process (or part of a process) needs to be swapped out to accommodate a new program. The replacement algorithm determines which are the partitions to be swapped out.

25.In loading programs into memory, what is the difference between load-time dynamic linking and run-time dynamic linking?
For load-time dynamic linking: Load module to be loaded is read into memory. Any reference to a target external module causes that module to be loaded and the references are updated to a relative address from the start base address of the application module.
With run-time dynamic loading: Some of the linking is postponed until actual reference during execution. Then the correct module is loaded and linked.

26.What are demand- and pre-paging?
With demand paging, a page is brought into memory only when a location on that page is actually referenced during execution. With pre-paging, pages other than the one demanded by a page fault are brought in. The selection of such pages is done based on common access patterns, especially for secondary memory devices.

27.Paging a memory management function, while multiprogramming a processor management function, are the two interdependent?
Yes.

28.What is page cannibalizing?
Page swapping or page replacements are called page cannibalizing.

29.What has triggered the need for multitasking in PCs?
Increased speed and memory capacity of microprocessors together with the support fir virtual memory and
Growth of client server computing

30.What are the four layers that Windows NT have in order to achieve independence?
Hardware abstraction layer
Kernel
Subsystems
System Services. 
Technical Operating Systems

31.What is SMP?
To achieve maximum efficiency and reliability a mode of operation known as symmetric multiprocessing is used. In essence, with SMP any process or threads can be assigned to any processor.

32.What are the key object oriented concepts used by Windows NT?
Encapsulation
Object class and instance

33.Is Windows NT a full blown object oriented operating system? Give reasons.
No Windows NT is not so, because its not implemented in object oriented language and the data structures reside within one executive component and are not represented as objects and it does not support object oriented capabilities .

34.What is a drawback of MVT?
It does not have the features like
ability to support multiple processors
virtual storage
source level debugging

35.What is process spawning?
When the OS at the explicit request of another process creates a process, this action is called process spawning.

How many jobs can be run concurrently on MVT?
15 jobs
List out some reasons for process termination.
Normal completion
Time limit exceeded
Memory unavailable
Bounds violation
Protection error
Arithmetic error
Time overrun
I/O failure
Invalid instruction
Privileged instruction
Data misuse
Operator or OS intervention
Parent termination.

What are the reasons for process suspension?
swapping
interactive user request
timing
parent process request

What is process migration?
It is the transfer of sufficient amount of the state of process from one machine to the target machine

What is mutant?
In Windows NT a mutant provides kernel mode or user mode mutual exclusion with the notion of ownership.

What is an idle thread?
The special thread a dispatcher will execute when no ready thread is found.

What is FtDisk?
It is a fault tolerance disk driver for Windows NT.

What are the possible threads a thread can have?
Ready
Standby
Running
Waiting
Transition
Terminated.

What are rings in Windows NT?
Windows NT uses protection mechanism called rings provides by the process to implement separation between the user mode and kernel mode.

What is Executive in Windows NT?
In Windows NT, executive refers to the operating system code that runs in kernel mode.

What are the sub-components of I/O manager in Windows NT?
Network redirector/ Server
Cache manager.
File systems
Network driver
Device driver

What are DDks? Name an operating system that includes this feature.
DDks are device driver kits, which are equivalent to SDKs for writing device drivers. Windows NT includes DDks.

What level of security does Windows NT meets?
C2 level security.
Technical Operating Systems

Physics questions and answers

Physics questions and answers

Q1. Two bodies changed from p1v1 to p2v2 state in two ways. The heat supplied is delta Q and work done is delta W
Then what is constant in these two processes

(a) delta q
(b) delta w
(c) delta q + delta w
(d) delta q - delta w

Ans. (d)


Q2. _______ have same atomic number and same mass number are

(a) Isotopes
(b) Isotones
(c) Isomers
(d) Isobars

Ans. (c)


Q3. When a free electron is placed in a plane of electro magnetic then it moves in

(a) in the direction of the electric field
(b) in the direction of magnetic field
(c) of propagation of wave
(d) of the plane containing magnetic field and propagation direction.


Q4. Name the phenomena in which one proton is jumped from one isomer to another isomer to create two different elements

(a) functional isomerisim
(b) sterio merisim
(c) tauto merisim
(d) penta merisim

Ans. (c)


Q5. In the below compounds which one has 40% C ,6.7% H and 53.3 % O what is its empherical formula

(a) CHO
(b) CH2
(c) C2H2O2
(d) C2H3O2

Ans: (b)


Q6. X rays are coming from X ray tube, the wavelength is _______ a certain wavelength/s

(a) below
(b) above
(c) inbetween
(d) out of

Ans. (c)


Q7. In a triode valve in order to increase the saturation current what has to be done

(a) increase plate voltage
(b) reduce distance between grid and plate
(c) increase cathode potential
(d) reduce grid potential

Ans. (d )


Q8. Seven different toys are distributed among 3 children how many different ways are possible?

(a) 7C3
(b) 7P3
(c) 3 7
(d) 7 3

Ans. (c)


Q9. A, B ans C are three speakers. They have to speak randomly along with another 5 speakers in a function.
A has to speak before B and B has to speak before C. What is the probability.

Ans. 1/6


Q10. If dy = (secx + ytanx)dx, Then the curve is

(a) x = ycosx
(b) x = ysinx
(c) x = ytanx
(d) x = ysecx

Ans. (a)


Q11. Two series are 16,21,26.... and 17,21,25.....
What is the sum of first hundred common numbers

(a) 101100
(b) 110100
(c) 101110
(d) 110101

Ans. (a)


Q12. There are two sections in a question paper each contain five questions. A students has to answer 6 questions.
Maximum no. of questions that can be answered from any section is 4. How many ways he can attempt the paper?

(a) 50
(b) 100
(c) 120
(d) 200

Ans. (d)


Q13. a and b are two numbers selected randomly from 1,2,3.... 25 what is the probability of a and b are not equal.

(a) 1/25
(b) 24/25
(c) 13/25
(d) 2/25

Ans. (b)


Q14. The sum of the series 1 + 1(1+1/n) + 3(1+1/n)2 + ..... is equal to?

Ans. n2


Q15. Two circles of different radii intersects each other what is the maximum no of intersections

(a) 0
(b) 1
(c) 2
(d) 3

Ans. (c)


Q16. If x= sin-1(t), y = log(1-t2), find d2y/dx2 when t=1/2

(a) 1
(b) 0
(c) -8/3
(d) -2/3

Ans. (c)


Q17. If x approaches infinity , then (òex dx )/( òe2xdx) is ?

(a) 1
(b) 0
(c) -1
(d) 2

Ans. (a)


Q18. If f(x)=1-cos(1-cosx)/x4 is continuos at f(0) then what is x

(a) 1
(b) 0
(c) 1/4
(d) -1/4

Ans. (c)


Q19. For the word SURITI, if you arrange the letters in dictionary order then what is its rank?

(a) 234
(b) 235
(c) 236
(d) 237

Ans. (c)


Q20. Period of sin ((2t + 3) / 6 pi)

(a) 6pi
(b) 6pi2
(c) 3pi

Ans. (b)


Q21 - Q23. Four questions given on the below data


X,Yand Z are senior engineers. A,B,C,D are junior engineers. Company wants to select 4 enginers. Two will be senior and two will be juniors. The company wants these engineers to work in the most productive way so they respect each person's likes/dislikes.

Y is not friends with A

Z is not friends with C

B is not friends with A

If B is selected then who will be the remaining 4 members ?

If C is selected, Z and ___ cannot be selected?

D is always selected if ___ is selected?


Q24. A speaks truth 70% of the times, B speaks truth 80% of the times.
What is the probability that both are contradicting each other is ?


Q25. ò((2x-3)/((x2 +x+1)2 )dx is ?


Q26. Ram starts from A walking 2 km North and turns right and walks 4 km and turns right again and walks 4 km and turns right again and walks 4 km and meets Radha at Bwalking in the opposite direction to Ram .
a) Which direction does Ram walk after the first turn?
b) Distance between A and B


Q27. If the equation x2 - 3x + a = 0 has the roots (0,1) then value of a is ?


Q28. A and B's temperature are 10°c and 20°c having same surface , then their ratio of rate of emmisions is ?


Q29. An atomic particle exists and has a particlular decay rate . It is in a train . When the train moves, a person observes for whether the decay rate

(a) increases
(b) decreases
(c) depend on the directions of movement of train


Q30. Which of the following exchanges positive ions

(a).cl-
(b) nh2-
(c) ch2

Ans. (b)


Q31. After execution of CMP, a instruction in Intel 8085 microprocessor

(a) ZF is set and CY is reset.
(b) ZF is set CY is unchanged
(c) ZF is reset, CY is set
(d) ZF is reset , CY is unchanged .

Ans. ZF is set and CY is reset


Q32. The best tool for editing a graphic image is ?


Q33. Network scheme defines
a.)one to one
b.) many to many
c.) one to ,many ?


Q34. A person wants to measures the length of a rod.First he measures with standing ideally then he maeasures by
moving parrel to the rod

(a)the length will decrease in second case
(b)length will be same
(c) length will increse in the second case.


Q35. One U-230 nucleus is placed in a train moving by velocity emiting alpha rays .When the train is at rest the
distance between nucleus and alpha particle is x . One passenger is observing the particle . When the train is moving
what is the distance between particle and nucleus ?

(a) x
(b) x + vt
(c) x - vt

Q36. What is the resulting solution when benzene and toluene are mixed ?


Q37. If the word FADENCOMT equals 345687921 then

What is FEAT

Find representation of 2998


Q38. Given 10 alphabets out of which 5 are to be chosen. How many words can be made with atleast one repetition.


Q39. Arrange by acidic values : phenol, nitrotolouene and o-cresol?


Q40. Find sum of 3 + 5/(1+22) + 7/(1 + 22 + 32) + ......

Ans. 3n/(1 + n)


The following are few sample questions that maybe asked in the software paper.We haven't been able to give the values in certain problems ; only the type of questions have been mentioned.

Q What sorting algos have their best and worst case times equal ?
Ans. O(nlogn) for mergesort and heap sort

Q. What page replacement algo . has minimumn number of page faults ?
Ans. Optimality algorithm

Q. What is the use of virtual base class in c++
Ans. Multiple lines between derived classes.

Q. Find the eccentricity of a given node in a directed graph

Q. Convert the infix to postfix for A-(B+C)*(D/E)
Ans. ABC+DE/*-

Q. What is swapping

Q. Assignment operator targets to
Ans. l-value

Q. A byte addressable computer has memory capacity of 2 power m Kbytes and can perform 2 power n operations
an instruction involving three operands and one operator needs maximum of ---bits
Ans. 3m + n

Q. In round robin scheduling, if time quatum is too large then it degenerates to
Ans. FCFS

Q. What is network schema?

Q. Packet Burst is ______

Q. Picard's method uses _______?
Ans. Successive Differentiation.



The following are few sample questions that maybe asked in the hardware paper. We haven't been able to give the values in certain problems ; only the type of questions have been mentioned.

Q. Concentration and restivity is given and conductivity is asked for ?

Q. R , resistance and C, capacitance is given ,find the frequency and Q factor of the crystal ?

Q. Critical frequency and angle theta is given ;.the max useable frequency is to be calculated

Q. Questions on parabolic reflector antenna's and half wave dipole antenna's design

Q. Ramp signal is generated from integrator .Whether it is a low or high pass filter .?

Q. Calculate FM bandwidth given max modulation frequency FM , max freq deviation , df and 8 pairs allowable side band component ?