Russell's Paradox

Russell's Paradox

© Copyright 2000, Jim Loy
Let you tell me a famous story:

There was once a barber. Some say that he lived in Seville. Wherever he lived, all of the men in this town either shaved themselves or were shaved by the barber. And the barber only shaved the men who did not shave themselves.

That is a nice story. But it raises the question: Did the barber shave himself? Let's say that he did shave himself. But we see from the story that he shaved only the men in town who did not shave themselves. Therefore, he did not shave himself. But we again see in the story that every man in town either shaved himself or was shaved by the barber. So he did shave himself. We have a contradiction. What does that mean?
Maybe it means that the barber lived outside of town. That would be a loophole, except that the story says that he did live in the town, maybe in Seville. Maybe it means that the barber was a woman. Another loophole, except that the story calls the barber "he." So that doesn't work. Maybe there were men who neither shaved themselves nor were shaved by the barber. Nope, the story says, "All of the men in this town either shaved themselves or were shaved by the barber." Maybe there were men who shaved themselves AND were shaved by the barber. After all, "either ... or" is a little ambiguous. But the story goes on to say, "The barber only shaved the men who did not shave themselves." So that doesn't work either. Often, when the above story is told, one of these last two loopholes is left open. So I had to be careful, when I wrote down the story.
Now we come to a really serious attempt to solve the above puzzle: Maybe there was no barber like the one described in the story. But the story said, "There was once a barber..." So there really was a barber like that, unless the story is a lie! That is the answer, isn't it? The story is a lie. Sorry about that. I told the story of a barber who could not possibly exist. I had good motives. But I guess I told a lie.
In logic, some statements are true (Jim is nearsighted), some are false (Jim eats squash). And a collection of statements, such as our story, is either consistent or inconsistent. The following pair of statements is inconsistent:

1. Jim likes vanilla ice cream with Smuckers Plum Jam on it!
2. Jim does not like vanilla ice cream with Smuckers Plum Jam on it.

They contradict one another. They cannot both be true. In fact, one of them is really really false. Well, our story of the barber is inconsistent. In logic, we don't say that it is a lie. We say that it is inconsistent. "Inconsistent" is much more descriptive, and it is not a sin.

---

The above story about the barber is the popular version of Russell's Paradox. The story was originally told by Bertrand Russell. And of course it has a simple solution. It is inconsistent. But the story is not really that simple. The story is a retelling of a problem in set theory.
In set theory, we have sets, collections of objects. These objects may be real physical objects (marbles) or not (cartoon characters, thoughts, or numbers). When we deal with a set, we normally write it down with brackets: {A, B, C}. That set contains three letters, A, B, and C. The set {B,C} is a subset of {A, B, C}. There is a special set with no elements, the empty set {} or ø, as the set of humans bigger than the earth, or the set of odd numbers divisible by two. Some sets contain infinitely many elements, as the set of all even numbers.
A set can contain sets. The set {{A, B, C}, {x, y}} contains two sets {A, B, C} and {x, y}. It also contains the empty set, by the way. All sets contain the empty set. We can define the set of all sets. This set contains {A, B, C} and {{A, B, C}, {x, y}} and every other possible set. Some sets contain themselves. The set of all red marbles does not contain itself, because it contains no sets at all, only marbles. Let's say that S is a set which contains S and {A, B}. Then this is S: {S, {A, B}}. It contains two sets, itself and {A, B}. The set of all sets obviously contains itself. Well, let's construct a very interesting set, the set of all sets which do not contain themselves.
There is something wrong here. Does "the set of all sets which do not contain themselves" sound like "the barber who shaves all men who do not shave themselves?" The story of the barber was inconsistent. The set of all sets which do not contain themselves is inconsistent for the same reason. Does the set of all sets which do not contain themselves actually contain itself, or not? If it contains itself, then it cannot contain itself. If it does not contain itself, then it must contain itself. It is inconsistent.
But where did we go wrong? Let's make some lists. A list is a special kind of set. But we know what a list is. A list may be clearer in our minds than a set. We cannot actually physically make infinite lists. But we can certainly define some of them, like the list of all even numbers. So we can deal with infinite lists. We can also make lists of lists. Here is such a list:

1. My shopping list
2. My email address list
3. David Letterman's list of Top Ten Whatevers

This list of lists is real. Now, if we allow infinite lists, then it is no stretch at all to produce the list of all lists, and even the list of all lists which do not contain themselves. And that list is inconsistent.
Well, maybe there are no infinite lists. There are infinite sets, for example, the set of all even numbers. And that is a list: the list of all even numbers. The concept of an infinite list is actually fairly simple.
So we have an inconsistent set. That is not all. We made no mistakes when we constructed the set of all sets which do not contain themselves. And that means that set theory is inconsistent. And that means that logic is inconsistent. And that means that all of mathematics, including algebra and geometry, is inconsistent.
It doesn't invalidate mathematics or logic or set theory. The Pythagorean theorem is still true. But there is some doubt. Kurt Godel (Gödel) proved that Number Theory (and by identical arguments, every branch of mathematics) is inconsistent. He converted Russell's Paradox, the set version, into a statement in Number Theory, and showed that Number Theory is inconsistent. This had huge repercussions in the world of mathematics. All of this leads to the following problem:

1. There are things that are true in mathematics (based on basic assumptions).
2. There are things that are false.
3. There are things that are true that can never be proved.
4. There are things that are false that can never be disproved.

And that is a problem, because we cannot ever tell if something is true unless we can prove it.

UGC NET

Related Pages: December 2008 Paper II Solution, December 2004 PaperII,

Graph Theory Notes and Previous years Q&A
 MCQ on Computer Organisation   MCQ on DBMS   MCQ on Web and Internet  Books on MCQ 
MCQ on Computer Science1    MCQ on Computer Science2       MCQ on Computer Science3

MODEL UGC -NET PAPER I

This sample paper in for Paper I of the UGC NET Exam which is common for all streams.
1. Which one of the following is the main objective of teaching?
(A) To give information related to the syllabus.
(B) To develop thinking power of students.
(C) To dictate notes to students.
(D) To prepare students to pass the examination.
2. Which one of the following is a good method of teaching?
(A) Lecture and Dictation
(B) Seminar and Project
(C) Seminar and Dictation
(D) Dictation and Assignment
3. Teacher uses teaching aids for
(A) Making teaching interesting
(B) Making teaching within understanding level of students
(C) Making students attentive.
(D) The sake of its use.
4. Effectiveness of teaching depends on
(A) Qualification of teacher
(B) Personality of teacher
(C) Handwriting of teacher
(D) Subject understanding of teacher
5. Which of the following is not characteristic of a good question paper?
(A) Objectivity
(B) Subjectivity
(C) No use of vague words
(D) Reliable.
6. A researcher is generally expected to:
(A) Study the existing literature in a field
(B) Generate new principles and theories
(C) Synthesize the idea given by others
(D) Evaluate the findings of a study
7. One of the essential characteristics of research is:
(A) Replicability
(B) Generalizability
(C) Usability
(D) Objectivity
8. The Government of India conducts Census after every 10 years. The method of research used in this process is:
(A) Case Study
(B) Developmental
(C) Survey
(D) Experimental
9. An academic association assembled at one place to discuss the progress of its work and future plans. Such an assembly is known as a
(A) Conference
(B) Seminar
(C) Workshop
(D) Symposium
10. An investigator studied the census date for a given area and prepared a write-up based on them. Such a write-up is called
(A) Research paper
(B) Article
(C) Thesis
(D) Research report
Read the following passage and answer the Question Nos. 11 to 15
The constitution guarantees every citizen the fundamental right to equality. Yet after 50 years of independence, just one perusal of the female infant mortality figures, the literacy rates and the employment opportunities for women is sufficient evidence that discrimination exists. Almost predictably, this gender, bias is evident in our political system as well. In the 13th Lok Sabha, there were only 43 women MPs out of total of 543; it is not a surprising figure, for never has women's representation in Parliament been more than 10 per cent.
Historically, the manifestos of major political have always encouraged women's participation. It has been merely a charade. So, women's organizations, denied a place on merit, opted for the last resort; a reservation of seats for women in parliament and State Assemblies. Parties, which look at everything with a vote bank in mind, seemed to endorse this. Alas, this too was a mirage.
But there is another aspect also. At a time when caste is the trump card, some politicians want the bill to include further quotas fro women from among minorities and backward castes. There is more to it. A survey shows that there is a general antipathy towards the bill. It is actually a classic case of doublespeak: in public, politicians were endorsing women's reservation but in the backrooms of Parliament, they were busy sabotaging it. The reasons are clear: Men just don't want to vacate their seats of power.
11. The problem raised in the passage reflects badly on our
(A) Political system
(B) Social behaviour
(C) Individual behaviour
(D) Behaviour of a group of people
12. According to the passage, political parties have mostly in mind
(A) Economic prosperity
(B) Vote bank
(C) People' welfare
(D) Patriotism
13. "Trump Card" means
(A) Trying to move a dead horse
(B) Playing the card cautiously
(C) Sabotaging all the moves by others
(D) Making the final jolt for success
14. The sentence "Men just don't want to vacate their seats of power" implies
(A) Lust for power
(B) Desire to serve the nation
(C) Conviction in one's own political abilities
(D) Political corruption
15. What is the percentage of women in the Lok Sabha
(A) 10
(B) 7. 91
(C) 43
(D) 9. 1
16. Informal communication network within the organization is knows as
(A) Interpersonal communication
(B) Intrapersonal Communication
(C) Mass Communication
(D) Grapevine Communication
17. TV Channel launched fro covering only Engineering and Technology subject is known as
(A) Gyan Darshan
(B) Vyas
(C) Eklavya
(D) Kisan
18. In which state the maximum number of periodicals are brought out for public information:
(A) Uttar Pradesh
(B) Tamil Nadu
(C) Kerala
(D) Punjab
19. The main objective of public broadcasting system i. e Prasar Bharti is
(A) Inform, Entertainment & Education
(B) Entertain, Information & Interaction
(C) Educate, Interact & entertain
(D) Entertainment only
20. The competerrcy of an effective communicator can be judged on the basis of:
(A) Personality of communicator
(B) Experience in the field
(C) Interactivity with target audience
(D) Meeting the needs of target audience.
21. Which one of the following belongs to the category of homogeneous date:
(A) Multi-storeyed houses in a colony
(B) Trees in a garden
(C) Vehicular traffic on a highway
(D) Student population in a class
22. In which of the following ways a theory is not different from a belief?
(A) Antecedent - consequent
(B) Acceptability
(C) Verifiability
(D) Demonstratability
23. The state - "Honesty is the best policy" is
(A) A fact
(B) An value
(C) An opinion
(D) A value judgement
24. Which one is like pillar, pole and standard?
(A) Beam
(B) Plank
(C) Shaft
(D) Timber
25. Following incomplete series is presented. Find out the number which should come at the place of question mark which will complete the series: 4, 16, 36, 64, ?
(A) 300
(B) 200
(C) 100
(D) 150
26. The following question is based on the diagram given below. If the two big circles represent animals living on soil and those living in water, and the small circle stands for the animals who both live on soil and in water, which figure represents the relationships among them.

27. Of the following statement, there are two statements both of which cannot be true but both can be false. Which are these two statements?
(i) All machines make noise
(ii) Some machines are noisy
(iii) No machine makes noise
(iv) Some machines are not noisy
(A) (i) and (ii)
(B) (iii) and (iv)
(C) (i) and (iii)
(D) (ii) and (iv)
28. In the following question a statement is followed by two assumptions.
(i) and (ii) . An assumption is something supposed or taken for granted.
Consider the statement and the following assumptions and decide which of the following assumptions is implicit in the statement.
Statement: We need not worry about errors but must try to learn from our errors.
Assumptions:
(i) Errors may take place when we are carrying out certain work.
(ii) We are capable of benefiting from the past and improve our chances of error-free work.
(A) Only assumption (i) is implicit
(B) Only assumption (ii) is implicit
(C) Either assumption (i) or (ii) is implicit
(D) Both the assumptions are implicit
29. The question below is followed by two arguments numbered (i) and (ii) Decide which of the arguments is 'strong' and which is 'weak'. Choose the correct answer from the given below Should the press exercise some self-restraint?
(i) Yes, they should not publish new items which may incite the readers to indulge in wrong practices.
(ii) No. it is the responsibility of the press to present the truth irrespective of the consequences.
(A) Only the argument (i) is strong
(B) Only the argument (ii) is strong
(C) Neither argument (i) nor (ii) is strong
(D) Both the arguments (i) and (ii) are strong
30. Study the argument and the inference drawn from that argument. Given below carefully.
Argument: Anything that goes up definitely falls down. Helicopter goes up. Inference: So the helicopter will definitely fall down.
What in your opinion is the inference drawn from the argument?
(A) Valid
(B) Invalid
(C) Doubtful
(D) Long drawn one
Four students W, X, Y, Z appeared in four papers, I, II, III and IV in a test. Their scores out of 100 are given below.

Students	Papers
	I	II	III	IV
W	60	81	45	55
X	59	43	51	A
Y	74	A	71	65
Z	72	76	A	68
Where 'A' stands for absent

Where 'A' stands for absent
Read the above table and answer below mentioned Questions 31 to 35
31. Which candidate has secured between 60-65% marks in aggregate
(A) W
(B) X
(C) Y
(D) Z
32. Who has obtained the lowest average in aggregate.
(A) W
(B) X
(C) Y
(D) Z
33. Who has obtained the highest average
(A) W
(B) X
(C) Y
(D) Z
34. In which paper the lowest marks were obtained by thecandiates
(A) I
(B) II
(C) III
(D) IV
35. Which candidate has secured the highest percentage in the papers appeared
(A) W
(B) X
(C) Y
(D) Z
36. ICT stands for
(A) Information common technology
(B) Information & communication technology
(C) Information and computer technology
(D) Inter connected technology
37. Computer Can
(A) Process both quantitative and qualitative information
(B) Store huge information
(C) Process information and fast accurately
(D) All the above.
38. Satellite Communication works through
(A) Rader
(B) Transponder
(C) Receptor
(D) Transmitter
39. A Computer is that machine which works more like a human brain. This definition of computer is
(A) Correct
(B) Incorrect
(C) Partially correct
(D) None of the above.
40. Information and communication technology includes
(A) E-mail
(B) Internet
(C) Education television
(D) All the above.
41. It is believed that our globe is warming progressively. This global warming will eventually result in.
(A) Increase in availability of usable land.
(B) Uniformity of climate at equator and poles.
(C) Fall in the sea level
(D) melting of polar ice.
42. In which parts of India ground water is affected with arsenic contamination?
(A) Haryana
(B) Andhra Pradesh
(C) Sikkim
(D) West Bengal
43. Sunderban in Hooghly delta is known for
(A) Grasslands
(B) Conifers
(C) Mangroves
(D) Arid forests
44. Sardar Sarover dam is located on the river
(A) Ganga
(B) Godavari
(C) Mahanadi
(D) Narmada
45. Which one of the following trees has medicinal value?
(A) Pine
(B) Teak
(C) Neem
(D) Oak
46. Which one of the following is not considered a part of technical education in India:
(A) Medical
(B) Management
(C) Pharmaceutical
(D) Aeronautical
47. Which of the following is a Central university
(A) Mumbai University
(B) Calcutta University
(C) Delhi University
(D) Madras University
48. Identify the main Principle on which the Parliamentary System Operates
(A) Responsibility of Executive to Legislature
(B) Supremacy of Parliament
(C) Supremacy of Judiciary
(D) Theory of Separation of Power
49. The reservation of seats for women in the Panchayat Raj Institutions is:
(A) 30 % of the total seats
(B) 33 % of the total seate
(C) 33% of the total population
(D) In Proportion to their population
50. Match list I with list II and select the correct answer from the code given below:
LIST ( Institutions)
LIST II( Locations)
1. Indian Veterinary Research Institute
(i) Pune
2. Institute of Armament Technology
(ii) Izat Nagar
3. Indian Institute of Science
(iii) Delhi
4. National Institute for Educational Pannesi
(iv) Bangalore and Administrators
(A) 1(ii), 2(i), 3(iv), 4(iii)
(B) 1(ii), 2(iv), 3(ii), 4(iii)
(C) 1(ii), 2(iii), 3(i), 4(iv)
(D) 1(iv), 2(iii), 3(ii), 4(i)
Source: Sample Paper based on questions provided by UGC Model Paper.
Answer Key:

1.	B	2.	B	3.	B	4.	D	5.	B	6.	B	7.	D	8.	C	9.	A	10.	B
11.	B	12.	B	13.	D	14.	A	15.	B	16.	D	17.	C	18.	C	19.	A	20.	D
21.	A	22.	B	23.	D	24.	A	25.	A	26.	D	27.	C	28.	D	29.	A	30.	D
31.	A	32.	B	33.	A	34.	B	35.	D	36.	B	37.	D	38.	B	39.	A	40.	D
41.	D	42.	D	43.	C	44.	D	45.	C	46.	A	47.	C	48.	A	49.	B	50.	A

Operating System Question and answer

Q: What are the basic functions of an operating system?

A: Operating system controls and coordinates the use of the hardware among the various applications programs for various uses. Operating system acts as resource allocator and manager. Since there are many possibly conflicting requests for resources the operating system must decide which requests are allocated resources to operating the computer system efficiently and fairly. Also operating system is control program which controls the user programs to prevent errors and improper use of the computer. It is especially concerned with the operation and control of I/O devices.

Q: Why paging is used?

A: Paging is solution to external fragmentation problem which is to permit the logical address space of a process to be noncontiguous, thus allowing a process to be allocating physical memory wherever the latter is available.
While running DOS on a PC, which command would be used to duplicate the entire diskette? diskcopy

Q: What resources are used when a thread created? How do they differ from those when a process is created?

A: When a thread is created the threads does not require any new resources to execute the thread shares the resources like memory of the process to which they belong to. The benefit of code sharing is that it allows an application to have several different threads of activity all within the same address space. Whereas if a new process creation is very heavyweight because it always requires new address space to be created and even if they share the memory then the inter process communication is expensive when compared to the communication between the threads.

Q: What is virtual memory?

A: Virtual memory is hardware technique where the system appears to have more memory that it actually does. This is done by time-sharing, the physical memory and storage parts of the memory one disk when they are not actively being used.

Q: What is Throughput, Turnaround time, waiting time and Response time?

A: Throughput – number of processes that complete their execution per time unit. Turnaround time – amount of time to execute a particular process. Waiting time – amount of time a process has been waiting in the ready queue. Response time – amount of time it takes from when a request was submitted until the first response is produced, not output (for time-sharing environment).

Q: What is the state of the processor, when a process is waiting for some event to occur?

A: Waiting state

Q: What is the important aspect of a real-time system or Mission Critical Systems?

A: A real time operating system has well defined fixed time constraints. Process must be done within the defined constraints or the system will fail. An example is the operating system for a flight control computer or an advanced jet airplane. Often used as a control device in a dedicated application such as controlling scientific experiments, medical imaging systems, industrial control systems, and some display systems. Real-Time systems may be either hard or soft real-time. Hard real-time: Secondary storage limited or absent, data stored in short term memory, or read-only memory (ROM), Conflicts with time-sharing systems, not supported by general-purpose operating systems. Soft real-time: Limited utility in industrial control of robotics, Useful in applications (multimedia, virtual reality) requiring advanced operating-system features.

Q: What is the difference between Hard and Soft real-time systems?

A: A hard real-time system guarantees that critical tasks complete on time. This goal requires that all delays in the system be bounded from the retrieval of the stored data to the time that it takes the operating system to finish any request made of it. A soft real time system where a critical real-time task gets priority over other tasks and retains that priority until it completes. As in hard real time systems kernel delays need to be bounded

Q: What is the cause of thrashing? How does the system detect thrashing? Once it detects thrashing, what can the system do to eliminate this problem?

A: Thrashing is caused by under allocation of the minimum number of pages required by a process, forcing it to continuously page fault. The system can detect thrashing by evaluating the level of CPU utilization as compared to the level of multiprogramming. It can be eliminated by reducing the level of multiprogramming.

Q: What is multi tasking, multi programming, multi threading?

A: Multi programming: Multiprogramming is the technique of running several programs at a time using timesharing. It allows a computer to do several things at the same time. Multiprogramming creates logical parallelism. The concept of multiprogramming is that the operating system keeps several jobs in memory simultaneously. The operating system selects a job from the job pool and starts executing a job, when that job needs to wait for any i/o operations the CPU is switched to another job. So the main idea here is that the CPU is never idle.

Multi tasking: Multitasking is the logical extension of multiprogramming .The concept of multitasking is quite similar to multiprogramming but difference is that the switching between jobs occurs so frequently that the users can interact with each program while it is running. This concept is also known as time-sharing systems. A time-shared operating system uses CPU scheduling and multiprogramming to provide each user with a small portion of time-shared system.

Multi threading: An application typically is implemented as a separate process with several threads of control. In some situations a single application may be required to perform several similar tasks for example a web server accepts client requests for web pages, images, sound, and so forth. A busy web server may have several of clients concurrently accessing it. If the web server ran as a traditional single-threaded process, it would be able to service only one client at a time. The amount of time that a client might have to wait for its request to be serviced could be enormous. So it is efficient to have one process that contains multiple threads to serve the same purpose. This approach would multithread the web-server process, the server would create a separate thread that would listen for client requests when a request was made rather than creating another process it would create another thread to service the request. To get the advantages like responsiveness, Resource sharing economy and utilization of multiprocessor architectures multithreading concept can be used.

Q: What is hard disk and what is its purpose?

A: Hard disk is the secondary storage device, which holds the data in bulk, and it holds the data on the magnetic medium of the disk.Hard disks have a hard platter that holds the magnetic medium, the magnetic medium can be easily erased and rewritten, and a typical desktop machine will have a hard disk with a capacity of between 10 and 40 gigabytes. Data is stored onto the disk in the form of files.

Q: What is fragmentation? Different types of fragmentation? 

A: Fragmentation occurs in a dynamic memory allocation system when many of the free blocks are too small to satisfy any request.
External Fragmentation: External Fragmentation happens when a dynamic memory allocation algorithm allocates some memory and a small piece is left over that cannot be effectively used. If too much external fragmentation occurs, the amount of usable memory is drastically reduced. Total memory space exists to satisfy a request, but it is not contiguous.
Internal Fragmentation: Internal fragmentation is the space wasted inside of allocated memory blocks because of restriction on the allowed sizes of allocated blocks. Allocated memory may be slightly larger than requested memory; this size difference is memory internal to a partition, but not being used

Q: What is DRAM? In which form does it store data?

A: DRAM is not the best, but it’s cheap, does the job, and is available almost everywhere you look. DRAM data resides in a cell made of a capacitor and a transistor. The capacitor tends to lose data unless it’s recharged every couple of milliseconds, and this recharging tends to slow down the performance of DRAM compared to speedier RAM types.

Q: What is Dispatcher?

A: Dispatcher module gives control of the CPU to the process selected by the short-term scheduler; this involves: Switching context, Switching to user mode, Jumping to the proper location in the user program to restart that program, dispatch latency – time it takes for the dispatcher to stop one process and start another running.

Q: What is CPU Scheduler?

A: Selects from among the processes in memory that are ready to execute, and allocates the CPU to one of them. CPU scheduling decisions may take place when a process: 1.Switches from running to waiting state. 2.Switches from running to ready state. 3.Switches from waiting to ready. 4.Terminates. Scheduling under 1 and 4 is non-preemptive. All other scheduling is preemptive.

Q: What is Context Switch?

A: Switching the CPU to another process requires saving the state of the old process and loading the saved state for the new process. This task is known as a context switch. Context-switch time is pure overhead, because the system does no useful work while switching. Its speed varies from machine to machine, depending on the memory speed, the number of registers which must be copied, the existed of special instructions(such as a single instruction to load or store all registers).

Q: What is cache memory?

A: Cache memory is random access memory (RAM) that a computer microprocessor can access more quickly than it can access regular RAM. As the microprocessor processes data, it looks first in the cache memory and if it finds the data there (from a previous reading of data), it does not have to do the more time-consuming reading of data from larger memory.

Q: What is a Safe State and what is its use in deadlock avoidance?

A: When a process requests an available resource, system must decide if immediate allocation leaves the system in a safe state. System is in safe state if there exists a safe sequence of all processes. Deadlock Avoidance: ensure that a system will never enter an unsafe state.

Q: What is a Real-Time System?

A: A real time process is a process that must respond to the events within a certain time period. A real time operating system is an operating system that can run real time processes successfully

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Operating System Question Answer (short type)

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 programduring 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 programand 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 aprocess' 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 oneØ process may use a critical resource at a time.
   HoldØ & Wait: A process may be allocated some resources while waiting for others.
   No Pre-emption: No resource can be forcible removed from aØ process holding it.
   Circular Wait: A closed chain of processes exist such that eachØ 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 includeØ program data, user stack area, and programs that may be modified.
   UserØ program: The instructions to be executed.
   System Stack: EachØ process has one or more LIFO stacks associated with it. Used to store parameters and calling addresses for procedure and system calls.
   Ø 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.)

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 cyclestealing 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:
DiscretionaryØ Access Control
Identification and AuthenticationØ
AuditingØ
Resource reuseØ

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:Ø 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.
GangØ 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 schedulingpredated this strategy.
Dedicated processor assignment: Provides implicitØ 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.
DynamicØ 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.
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<Tj or (b) if Ti=Tj and i<j.

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.

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.

36. How many jobs can be run concurrently on MVT?
15 jobs

37. 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.

38. What are the reasons for process suspension?

1. swapping

2. interactive user request

3. timing

4. parent process request

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

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

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

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

43. What are the possible threads a thread can have?
ReadyØ
StandbyØ
RunningØ
WaitingØ
TransitionØ
Terminated.Ø

44. 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.

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

46. What are the sub-components of I/O manager in Windows NT?
Network redirector/ ServerØ
Cache manager.Ø
File systemsØ
Network driverØ
Device driverØ

47. 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.

48. What level of security does Windows NT meets?
C2 level security.

1. What are the basic functions of an operating system? - Operating system controls and coordinates the use of the hardware among the various applications programs for various uses. Operating system acts as resource allocator and manager. Since there are many possibly conflicting requests for resources the operating system must decide which requests are allocated resources to operating the computer system efficiently and fairly. Also operating system is control program which controls the user programs to prevent errors and improper use of the computer. It is especially concerned with the operation and control of I/O devices.

2. Why paging is used? - Paging is solution to external fragmentation problem which is to permit the logical address space of a process to be noncontiguous, thus allowing a process to be allocating physical memory wherever the latter is available.

3. While running DOS on a PC, which command would be used to duplicate the entire diskette? diskcopy

4. What resources are used when a thread created? How do they differ from those when a process is created? - When a thread is created the threads does not require any new resources to execute the thread shares the resources like memory of the process to which they belong to. The benefit of code sharing is that it allows an application to have several different threads of activity all within the same address space. Whereas if a new process creation is very heavyweight because it always requires new address space to be created and even if they share the memory then the inter process communication is expensive when compared to the communication between the threads.

5. What is virtual memory? - Virtual memory is hardware technique where the system appears to have more memory that it actually does. This is done by time-sharing, the physical memory and storage parts of the memory one disk when they are not actively being used.

6. What is Throughput, Turnaround time, waiting time and Response time? - Throughput – number of processes that complete their execution per time unit. Turnaround time – amount of time to execute a particular process. Waiting time – amount of time a process has been waiting in the ready queue. Response time – amount of time it takes from when a request was submitted until the first response is produced, not output (for time-sharing environment).

7. What is the state of the processor, when a process is waiting for some event to occur? - Waiting state

8. What is the important aspect of a real-time system or Mission Critical Systems? - A real time operating system has well defined fixed time constraints. Process must be done within the defined constraints or the system will fail. An example is the operating system for a flight control computer or an advanced jet airplane. Often used as a control device in a dedicated application such as controlling scientific experiments, medical imaging systems, industrial control systems, and some display systems. Real-Time systems may be either hard or soft real-time. Hard real-time: Secondary storage limited or absent, data stored in short term memory, or read-only memory (ROM), Conflicts with time-sharing systems, not supported by general-purpose operating systems. Soft real-time: Limited utility in industrial control of robotics, Useful in applications (multimedia, virtual reality) requiring advanced operating-system features.

9. What is the difference between Hard and Soft real-time systems? - A hard real-time system guarantees that critical tasks complete on time. This goal requires that all delays in the system be bounded from the retrieval of the stored data to the time that it takes the operating system to finish any request made of it. A soft real time system where a critical real-time task gets priority over other tasks and retains that priority until it completes. As in hard real time systems kernel delays need to be bounded

10. What is the cause of thrashing? How does the system detect thrashing? Once it detects thrashing, what can the system do to eliminate this problem? - Thrashing is caused by under allocation of the minimum number of pages required by a process, forcing it to continuously page fault. The system can detect thrashing by evaluating the level of CPU utilization as compared to the level of multiprogramming. It can be eliminated by reducing the level of multiprogramming.

11. What is multi tasking, multi programming, multi threading? - Multi programming: Multiprogramming is the technique of running several programs at a time using timesharing. It allows a computer to do several things at the same time. Multiprogramming creates logical parallelism. The concept of multiprogramming is that the operating system keeps several jobs in memory simultaneously. The operating system selects a job from the job pool and starts executing a job, when that job needs to wait for any i/o operations the CPU is switched to another job. So the main idea here is that the CPU is never idle. Multi tasking: Multitasking is the logical extension of multiprogramming .The concept of multitasking is quite similar to multiprogramming but difference is that the switching between jobs occurs so frequently that the users can interact with each program while it is running. This concept is also known as time-sharing systems. A time-shared operating system uses CPU scheduling and multiprogramming to provide each user with a small portion of time-shared system. Multi threading: An application typically is implemented as a separate process with several threads of control. In some situations a single application may be required to perform several similar tasks for example a web server accepts client requests for web pages, images, sound, and so forth. A busy web server may have several of clients concurrently accessing it. If the web server ran as a traditional single-threaded process, it would be able to service only one client at a time. The amount of time that a client might have to wait for its request to be serviced could be enormous. So it is efficient to have one process that contains multiple threads to serve the same purpose. This approach would multithread the web-server process, the server would create a separate thread that would listen for client requests when a request was made rather than creating another process it would create another thread to service the request. To get the advantages like responsiveness, Resource sharing economy and utilization of multiprocessor architectures multithreading concept can be used.

12. What is hard disk and what is its purpose? - Hard disk is the secondary storage device, which holds the data in bulk, and it holds the data on the magnetic medium of the disk.Hard disks have a hard platter that holds the magnetic medium, the magnetic medium can be easily erased and rewritten, and a typical desktop machine will have a hard disk with a capacity of between 10 and 40 gigabytes. Data is stored onto the disk in the form of files.

13. What is fragmentation? Different types of fragmentation? - Fragmentation occurs in a dynamic memory allocation system when many of the free blocks are too small to satisfy any request. External Fragmentation: External Fragmentation happens when a dynamic memory allocation algorithm allocates some memory and a small piece is left over that cannot be effectively used. If too much external fragmentation occurs, the amount of usable memory is drastically reduced. Total memory space exists to satisfy a request, but it is not contiguous. Internal Fragmentation: Internal fragmentation is the space wasted inside of allocated memory blocks because of restriction on the allowed sizes of allocated blocks. Allocated memory may be slightly larger than requested memory; this size difference is memory internal to a partition, but not being used

14. What is DRAM? In which form does it store data? - DRAM is not the best, but it’s cheap, does the job, and is available almost everywhere you look. DRAM data resides in a cell made of a capacitor and a transistor. The capacitor tends to lose data unless it’s recharged every couple of milliseconds, and this recharging tends to slow down the performance of DRAM compared to speedier RAM types.

15. What is Dispatcher? - Dispatcher module gives control of the CPU to the process selected by the short-term scheduler; this involves: Switching context, Switching to user mode, Jumping to the proper location in the user program to restart that program, dispatch latency – time it takes for the dispatcher to stop one process and start another running.

16. What is CPU Scheduler? - Selects from among the processes in memory that are ready to execute, and allocates the CPU to one of them. CPU scheduling decisions may take place when a process: 1.Switches from running to waiting state. 2.Switches from running to ready state. 3.Switches from waiting to ready. 4.Terminates. Scheduling under 1 and 4 is non-preemptive. All other scheduling is preemptive.

17. What is Context Switch? - Switching the CPU to another process requires saving the state of the old process and loading the saved state for the new process. This task is known as a context switch. Context-switch time is pure overhead, because the system does no useful work while switching. Its speed varies from machine to machine, depending on the memory speed, the number of registers which must be copied, the existed of special instructions(such as a single instruction to load or store all registers).

18. What is cache memory? - Cache memory is random access memory (RAM) that a computer microprocessor can access more quickly than it can access regular RAM. As the microprocessor processes data, it looks first in the cache memory and if it finds the data there (from a previous reading of data), it does not have to do the more time-consuming reading of data from larger memory.

19. What is a Safe State and what is its use in deadlock avoidance? - When a process requests an available resource, system must decide if immediate allocation leaves the system in a safe state. System is in safe state if there exists a safe sequence of all processes. Deadlock Avoidance: ensure that a system will never enter an unsafe state.

20. What is a Real-Time System? - A real time process is a process that must respond to the events within a certain time period. A real time operating system is an operating system that can run real time processes successfully