SHIVALIK COLLEGE OF ENGINEEREING DEHRADUN

[DEPARTMENT OF COMPUTER SCIENCE & ENGINEERING ]

Operating Systems Interview Questions and Answers

1. What is an operating system? An operating system is a program that acts as an intermediary between the user and the computer hardware. The purpose of an OS is to provide a convenient environment in which user can execute programs in a convenient and efficient manner. It is a resource allocator responsible for allocating system resources and a control program which controls the operation of the computer hardware.

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. Explain the concept of the batched operating systems? In batched operating system the users gives their jobs to the operator who sorts the programs according to their requirements and executes them. This is time consuming but makes the CPU busy all the time.

4. What is purpose of different operating systems? The machine purpose workstation individual usability &resources utilization mainframe optimize utilization of hardware PC support complex games, business application Hand held PCs Easy interface & min. power consumption.

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 are the various components of a computer system?

The hardware

The operating system

The application programs

The users.

8. What is a Real-Time System?

A real time process is a process that must respond to the event switch in a certain

Time period. A real time operating system is an operating system that can run real

Time processes successfully.

9. Explain the concept of the Distributed systems?

Distributed systems work in a network. They can share the network resources,

communicate with each other.

10. What is SCSI?

SCSI - Small computer systems interface is a type of interface used for computer

components such as hard drives, optical drives, scanners and tape drives. It is a

competing technology to standard IDE (Integrated Drive Electronics).

11. What is a sector?

Smallest addressable portion of a disk.

12. What are the different operating systems?

Batched operating systems

Multi-programmed operating systems

Timesharing operating systems

Distributed operating systems

Real-time operating systems.

13. What is busy waiting?

The repeated execution of a loop of code while waiting for an event to occur is called

busy waiting.

14. What are system calls?

System calls provide the interface between a process and the operating system.

System calls for modern Microsoft windows platforms are part of the win32 API,

which is available for all the compilers written for Microsoft windows.

15. What are various scheduling queues?

Job queue

Ready queue

Device queue

16. What are java threads?

Java is one of the small number of languages that support at the language level for

the creation and management of threads. However, because threads are managed by

the java virtual machine (JVM), not by a user-level library or kernel, it is difficult to

classify Java threads as either user- or kernel-level.

17. What are types of threads?

User thread

Kernel thread

18. What is a semaphore?

It is a synchronization tool used to solve complex critical section problems. A

semaphore is an integer variable that, apart from initialization, is accessed only

through two standard atomic operations: Wait and Signal.

19. What is a deadlock?

Deadlock is a situation where a group of processes are all blocked and none of them

can become unblocked until one of the other becomes unblocked. The simplest

deadlock is two processes each of which is waiting for a message from the other.

20. 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.

21. 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.

22. What are the states of a process?

New

Running

Waiting

Ready

Terminated

23. What is a binary semaphore?

A binary semaphore is one, which takes only 0 and 1 as values. They are used to

Implement mutual exclusion and synchronize concurrent processes.

24. What is a job queue?

When a process enters the system it is placed in the job queue.

25. What is a ready queue?

The processes that are residing in the main memory and are ready and waiting to

execute are kept on a list called the ready queue.

26. 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.

27. What are the operating system components?

Process management

Main memory management

File management

I/O system management

Secondary storage management

Networking

Protection system

Command interpreter system

28. What is mutex?

Mutex is a program object that allows multiple program threads to share the same

resource, such as file access, but not simultaneously. When a program is started a

mutex is created woth a unique name. After this stage, any thread that needs the

resource must lock the mutex from other threads while it is using the resource. the

mutex is set to unlock when the data is no longer needed or the routine is finished.

29. What is Marshalling?

The process of packaging and sending interface method parameters across thread or

process boundaries.

30. What are residence monitors?

Early operating systems were called residence monitors.

31. Why thread is called as a lightweight process?

It is called light weight process to emphasize the fact that a thread is like a process

but is more efficient and uses fewer resources( n hence “lighter”)and they also share

the address space.

32. What are operating system services?

Program execution

I/O operations

File system manipulation

Communication

Error detection

Resource allocation

Accounting

Protection

33. What is a process?

A program in execution is called a process. Or it may also be called a unit of work. A

process needs some system resources as CPU time, memory, files, and i/o devices to

accomplish the task. Each process is represented in the operating system by a

process control block or task control block (PCB).Processes are of two types

Operating system processes

User processes

34. What are the different job scheduling in operating systems?

Scheduling is the activity of the deciding when process will receive the resources

they request.

FCFS ---> FCSFS stands for First Come First Served. In FCFS the job that has been

waiting the longest is served next.

Round Robin Scheduling--->Round Robin scheduling is a scheduling method

where each process gets a small quantity of time to run and then it is preempted and

the next process gets to run. This is called time-sharing and gives the effect of all the

processes running at the same time

Shortest Job First ---> The Shortest job First scheduling algorithm is a

nonpreemptive scheduling algorithm that chooses the job that will execute the

shortest amount of time.

Priority Scheduling--->Priority scheduling is a scheduling method where at all

times the highest priority process is assigned the resource.

35. What is dual-mode operation?

In order to protect the operating systems and the system programs from the

malfunctioning programs the two mode operations were evolved

System mode

User mode.

36. What is a device queue?

A list of processes waiting for a particular I/O device is called device queue.

37. What are the different types of Real-Time Scheduling?

Hard real-time systems required to complete a critical task within a guaranteed

amount of time.

Soft real-time computing requires that critical processes receive priority over less

fortunate ones.

38. What is starvation ?

Starvation is a resource management problem where a process does not get the

resources it needs for a long time because the resources are being allocated to other

processes.

39. What is a long term scheduler & short term schedulers?

Long term schedulers are the job schedulers that select processes from the job

queue and load them into memory for execution.

The Short term schedulers are the CPU schedulers that select a process form the

ready queue and allocate the CPU to one of them.

40. What is fragmentation?

Fragmentation occurs in a dynamic memory allocation system when many of the free

blocks are too small to satisfy any request.

41. What is context switching?

Transferring the control from one process to other process requires saving the state

of the old process and loading the saved state for new process. This task is known as

context switching.

42. What is relative path and absolute path?

Absolute path-- Exact path from root directory.

Relative path-- Relative to the current path.

43. What are the disadvantages of context switching?

Time taken for switching from one process to other is pure over head. Because the

system does no useful work while switching. So one of the solutions is to go for

threading when ever possible.

44. What is the state of the processor, when a process is waiting for some event

to occur?

Waiting state

45. What is the difference between Primary storage and secondary storage?

Main memory - only large storage media that the CPU can access directly.

Secondary storage - extension of main memory that provides large nonvolatile

storage capacity.

46. What is process synchronization?

A situation, where several processes access and manipulate the same data

concurrently and the outcome of the execution depends on the particular order in

which the access takes place, is called race condition. To guard against the race

condition we need to ensure that only one process at a time can be manipulating the

same data. The technique we use for this is called process synchronization.

47. What is a data register and address register?

Data registers - can be assigned to a variety of functions by the programmer. They

can be used with any machine instruction that performs operations on data.

Address registers - contain main memory addresses of data and instructions or

they contain a portion of the address that is used in the calculation of the complete

addresses.

48. What are deadlock prevention techniques?

Mutual exclusion

Hold and wait

No preemption

Circular wait

49. What is the difference between Complier and Interpreter?

An interpreter reads one instruction at a time and carries out the actions implied by

that instruction. It does not perform any translation. But a compiler translates the

entire instructions.

50. 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.

51. What is the difference between microkernel and macro kernel?

Micro-Kernel : A micro-kernel is a minimal operating system that performs only the essential functions of an operating system. All other

operating system functions are performed by system processes. Monolithic : A monolithic operating system is one where all operating system code is in a single executable image and all operating system code runs in system mode.

52. What is DRAM?

Dynamic Ram stores the data in the form of Capacitance, and Static RAM stores the data in Voltages.

53. What are the different functions of Scheduler?

Scheduler deals with the problem of deciding which of the process in the ready queue is to be allocated the CPU. Short Term Schedulers, Long Term Schedulers

54. 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.

55. 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.

56. What is cache-coherency?

In a multiprocessor system there exist several caches each may containing a copy of

same variable A. Then a change in one cache should immediately be reflected in all

other caches this process of maintaining the same value of a data in all the caches s

called cache-coherency.

57. What are the benefits of multithreaded programming?

Responsiveness

Resources sharing

Economy

Utilization of multiprocessor architectures.

********************Set2****************** 1) Explain the main purpose of an operating system?

Operating systems exist for two main purposes. One is that it is designed to make sure a computer system performs well by managing its computational activities. Another is that it provides an environment for the development and execution of programs. 2) What is demand paging? Demand paging is a system where in area of memory that are not currently being used are swapped to disk to make room for an application’s need.

3) What are the advantages of a multiprocessor system? With an increased number of processors, there is considerable increase in throughput. It can also save more money because they can share resources. Finally, overall reliability is increased as well.

4) What is kernel? Kernel is the core of every operating system. It connects applications to the actual processing of data. It also manages all communications between software and hardware components to ensure usability and reliability.

5) What are real-time systems? Real-time systems are used when rigid time requirements have been placed on the operation of a processor. It has well defined and fixed time constraints.

6) What is virtual memory? Virtual memory is a memory management technique for letting processes execute outside of memory. This is very useful especially is an executing program cannot fit in the physical memory.

7) Describe the objective of multiprogramming. The main objective of multiprogramming is to have process running at all times. With this design, CPU utilization is said to be maximized.

8 ) What are time sharing systems? In a Time sharing system, the CPU executes multiple jobs by switching among them, also known as multitasking. This process happens so fast that users can actually interact with each program while it is running.

9) What is SMP? SMP is short for Symmetric Multiprocessing, and is the most common type of multiple-processor systems. In this system, each processor runs an identical copy of the operating system, and these copies communicate with one another as needed.

10) How are server systems classified? Server systems can be classified as either computer-server systems or file server systems. In the first case, an interface is made available for clients to send requests to perform an action. In the second case, provisions are available for clients to create, access and update files.

11) What is asymmetric clustering? In asymmetric clustering, a machine is in a state known as hot standby mode where it does nothing but to monitor the active server. That machine takes the active server’s role should the server fails.

12) What is a thread? A thread is a basic unit of CPU utilization. In general, a thread is composed of a thread ID, program counter, register set and the stack.

13) Give some benefits of multithreaded programming. – there is an increased responsiveness to the user – resource sharing within the process – economy – utilization of multiprocessing architecture

14) Briefly explain FCFS. FCFS is short for First-come, first-served, and is one type of scheduling algorithm. In this scheme, the process that requests the CPU first is allocated the CPU first. Implementation is managed by a FIFO queue.

15) What is RR scheduling algorithm? RR (round-robin) scheduling algorithm is primarily aimed for time-sharing systems. A circular queue is setup in such a way that the CPU scheduler goes around that queue, allocating CPU to each process for a time interval of up to around 10 to 100 milliseconds.

16) What necessary conditions can lead to a deadlock situation in a system? Deadlock situations occur when four conditions occur simultaneously in a system: Mutual exclusion; Hold and Wait; No preemption; and Circular wait.

17) Enumerate the different RAID levels. RAID 0 – Non-redundant striping RAID 1 – Mirrored Disks RAID 2 – Memory-style error-correcting codes RAID 3 – Bit-interleaved Parity RAID 4 – Block-interleaved Parity RAID 5 – Block-interleaved distributed Parity RAID 6 – P+Q Redundancy

18) Describe Banker’s algorithm

Bankers Algorithm

Banker’s algorithm is one form of deadlock-avoidance in a system. It gets its name from a banking system wherein the bank never allocates available cash in such a way that it can no longer satisfy the needs of all of its customers.

19) What factors determine whether a detection-algorithm must be utilized in a deadlock avoidance system? One is that it depends on how often a deadlock is likely to occur under the implementation of this algorithm. The other has to do with how many processes will be affected by deadlock when this algorithm is applied.

20) Differentiate logical from physical address space. Logical address refers to the address that is generated by the CPU. On the other hand, physical address refers to the address that is seen by the memory unit.

21) How does dynamic loading aid in better memory space utilization? With dynamic loading, a routine is not loaded until it is called. This method is especially useful when large amounts of code are needed in order to handle infrequently occurring cases such as error routines.

22) What are overlays? Overlays are used to enable a process to be larger than the amount of memory allocated to it. The basic idea of this is that only instructions and data that are needed at any given time are kept in memory.

23) What is the basic function of paging? Paging is a memory management scheme that permits the physical-address space of a process to be noncontiguous. It avoids the considerable problem of having to fit varied sized memory chunks onto the backing store.

24) What is fragmentation? Fragmentation is memory wasted. It can be internal if we are dealing with systems that have fixed-sized allocation units, or external if we are dealing with systems that have variable-sized allocation units.

25) How does swapping result in better memory management?

During regular intervals that are set by the operating system, processes can be copied from main memory to a backing store, and then copied back later. Swapping allows more processes to be run that can fit into memory at one time.

26) Give an example of a Process State. – New State – means a process is being created – Running – means instructions are being executed – Waiting – means a process is waiting for certain conditions or events to occur – Ready – means a process is waiting for an instruction from the main processor – Terminate – means a process is done executing

27) What is a socket? A socket provides a connection between two applications. Each endpoint of a communication is a socket.

28) What is Direct Access Method? Direct Access method is based on a disk model of a file, such that it is viewed as a numbered sequence of blocks or records. It allows arbitrary blocks to be read or written. Direct access is advantageous when accessing large amounts of information.

29) When does trashing occur? Trashing refers to an instance of high paging activity. This happens when it is spending more time paging instead of executing.

30) What is the best page size when designing an operating system? The best paging size varies from system to system, so there is no single best when it comes to page size. There are different factors to consider in order to come up with a suitable page size, such as page table, paging time, and its effect on the overall efficiency of the operating system.

31) When designing the file structure for an operating system, what attributes are considered? Typically, the different attributes for a file structure are naming, identifier, supported file types, and location for the files, size, and level of protection.

32) What is root partition? Root partition is where the operating system kernel is located. It also contains other potentially important system files that are mounted during boot time.

33) What are device drivers? Device drivers provides a standard means of representing I/O devices that maybe manufactured by different companies. This prevents conflicts whenever such devices are incorporated in a systems unit.

34) What are the primary functions of VFS? VFS, or Virtual File System, separates file system generic operations from their implementation by defining a clean VFS interface. It is also based on a file-representation structure known as vnode, which contains a numerical designator needed to support network file systems.

35) What are the different types of CPU registers in a typical operating system design? – Accumulators – Index Registers – Stack Pointer – General Purpose Registers

36) What is the purpose of an I/O status information? I/O status information provides info about which I/O devices are to be allocated for a particular process. It also shows which files are opened, and other I/O device state.

37) What is multitasking? Multitasking is the process within an operating system that allows the user to run several applications at the same time. However, only one application is active at a time for user interaction, although some applications can run “behind the scene”.

38) What are some pros and cons of a command line interface? A command line interface allows the user to type in commands that can immediately provide results. Many seasoned computer users are well accustomed to using the command line because they find it quicker and simpler. The main problem with a command line interface is that users have to be familiar with the commands, including the switches and parameters that come with it. This is a downside for people who are not fond of memorizing commands.

39) What is caching? Caching is the processing of utilizing a region of fast memory for a limited data and process. A cache memory is usually much efficient because of its high access speed.

40) What is spooling? Spooling is normally associated with printing. When different applications want to send an output to the printer at the same time, spooling takes all of these print jobs into a disk file and queues them accordingly to the printer.

41) What is an Assembler? An assembler acts as a translator for low level language. Assembly codes, written using mnemonic commands are translated by the Assembler into machine language.

42) What are interrupts? Interrupts are part of a hardware mechanism that sends a notification to the CPU when it wants to gain access to a particular resource. An interrupt handler receives this interrupt signal and “tells” the processor to take action based on the interrupt request.

43) What is GUI? GUI is short for Graphical User Interface. It provides users with an interface wherein actions can be performed by interacting with icons and graphical symbols. People find it easier to interact with the computer when in a GUI especially when using the mouse. Instead of having to remember and type commands, users just click on buttons to perform a process.

44) What is preemptive multitasking? Preemptive multitasking allows an operating system to switch between software programs. This in turn allows multiple programs to run without necessarily taking complete control over the processor and resulting in system crashes.

45) Why is partitioning and formatting a prerequisite to installing an operating system? Partitioning and formatting creates a preparatory environment on the drive so that the operating system can be copied and installed properly. This includes allocating space on the drive, designating a drive name, determining and creating the appropriate file system structure.

46) What is plumbing / piping? It is the process of using the output of one program as an input to another. For example, instead of sending the listing of a folder or drive to the main screen, it can be piped and sent to a file, or sent to the printer to produce a hard copy.

47) What is NOS? NOS is short for Network Operating System. It is a specialized software that will allow a computer to communicate with other devices over the network, including file/folder sharing.

48) Differentiate internal commands from external commands. Internal commands are built-in commands that are already part of the operating system. External commands are separate file programs that are stored in a separate folder or directory.

49) Under DOS, what command will you type when you want to list down the files in a directory, and at the same time pause after every screen output? a) dir /w b) dir /p c) dir /s d) dir /w /p

Answer: d) dir /w /p

50) How would a filenamed EXAMPLEFILE.TXT appear when viewed under the DOS command console operating in Windows 98? The filename would appear as EXAMPL~1.TXT. The reason behind this is that filenames under this operating system is limited to 8 characters when working under DOS environment.

51):-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.

52). 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.

53). 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.

54). 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.

55). What is the Translation Look aside 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.

56). 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.)

57). When is a system in safe state?

The set of dispatch able 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

58). 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.

59). 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.

.

60). 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.

61). 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.

62):- 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.

63);-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.

64):-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.

65). 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.

66). 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.

67). 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.

68). 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.

69). 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 the partitions to be swapped out are.

70). 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.

71). What are demand-paging 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.

72). Paging a memory management function, while multiprogramming a processor management function, are the two interdependent?

Yes.

73). What is page cannibalizing?

Page swapping or page replacements are called page cannibalizing.

74). 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

75). What are the four layers that Windows NT have in order to achieve independence?

Hardware abstraction layer

Kernel

Subsystems

System Services.

76). 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.

77). What are the key object oriented concepts used by Windows NT?

Encapsulation, Object class and instance.

78). 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.

79). What is a drawback of MVT?

It does not have the features like

Ability to support multiple processors

Virtual storage

Source level debugging

80). What is process spawning?

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

81). How many jobs can be run concurrently on MVT?

15 jobs.

82). List out some reasons for process termination.

1. Normal completion 2. Time limit exceeded 3. Memory unavailable

4. Bounds violation 5. Protection error 6. Arithmetic error 7. Time overrun 8. I/O failure 9. Invalid instruction 10. Privileged instruction 11. Data misuse 12. Operator or OS intervention 13. Parent termination.

83). What are the reasons for process suspension?

1. swapping 2. interactive user request 3. timing 4. parent process request

84). What is process migration?

It is the transfer of sufficient amount of the state of process from one machine to the target machine.

85). What is mutant?

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

86). What is an idle thread?

The special thread a dispatcher will execute when no ready thread is found.

87). 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.

88). what is FtDisk?

It is a fault tolerance disk driver for Windows NT.

89). what are the possible threads a thread can have?

1. Ready 2. Standby 3. Running 4. Waiting 5. Transition 6. Terminated

90):-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.

91. 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.

92. 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.

93. What are the stipulations of C2 level security?

C2 level security provides for:

1. Discretionary Access Control 2. Identification and Authentication 3. Auditing 4. Resource reuse

94. 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.

95. What is Executive in Windows NT?

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

96. What are the sub-components of I/O manager in Windows NT?

1. Network redirector/ Server 2. Cache manager. 3. File systems 4. Network driver 5. Device driver

97. 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.

98. What level of security does Windows NT meets?

C2 level security.

Prepared by:-

KRISHNA BALLABH GUPTA [CSE 3RD Year].

SHIVALIK COLLEGE OF ENGINEERING DEHRADUN