DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING 2 MARKS AND 11 MARKS FOR ALL UNITS UNIT I

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1 DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING Subject Name: OPERATING SYSTEMS Subject Code: CS T51 2 MARKS AND 11 MARKS FOR ALL UNITS UNIT I Introduction: Mainframe Systems Desktop Systems Multiprocessor Systems Distributed Systems Clustered Systems - Real Time Systems Hardware Protection System Components Handheld Systems - Operating System Services System Calls System Programs Process Concept Process Scheduling Operations on Processes Cooperating Processes Inter-process Communication. 1. What is an operating system? PART A 2 MARK QUESTIONS An operating system is a program that manages the computer hardware. It also provides a basis for application program and acts as an intermediary between a user of a computer and the computer hardware. 2. What is context switch? (April 2016) 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. 3. Differentiate multiprogramming and multiprocessor operating system. (April 2016)

2 Multiprocessor systems (also known as parallel systems or tightly coupled systems have more than one processor in close communication, sharing the computer bus, the clock, and sometimes memory and peripheral devices. Multiprogramming increases CPU utilization by organizing jobs so that the CPU always has one to execute. In a multiprogramming system, the operating system simply switches to, and executes, another job. As long as at least one job needs to execute, the CPU is never idle. 4. Name any three components of the system. (NOVEMBER 2015) a. the hardware b. the operating system c. the application programs 5. What are the components of a computer system? A computer system can be divided into four components namely: a. the hardware b. the operating system c. the application programs d. the users 6. Name the five main components of an operating system. Process management Memory management Disk and file systems Networking Security 7. List out the major advantages of multiprocessor system? (NOVEMBER 2010),( APRIL/MAY 2014) Multiprocessor systems have three main advantages. Increased throughput. By increasing the number of processors, we hope to get more work done in less time. The speed-up ratio with N processors is not N; rather, it is less than N. Economy of scale. Multiprocessor systems can save more money than multiple single-processor systems, because they can share peripherals, mass storage, and power supplies. Increased reliability. If functions can be distributed properly among several processors, then the failure of one processor will not halt the system, only

3 slow it down. If we have ten processors and one fails, then each of the remaining nine processors must pick up a share of the work of the failed processor. This ability to continue providing service proportional to the level of surviving hardware is called graceful degradation. Systems designed for graceful degradation are also called fault tolerant. 8. Write the operating system services convenient to the users. (NOVEMBER 2010) Program execution: The system must be able to load a program into memory and to run that program. I/O operations: A running program may require I/O. This I/O may involve a file or an I/O device. For specific devices, special functions may be desired (such as to rewind a tape drive, or to blank a CRT screen). File-system manipulation: Obviously, programs need to read and write files. Programs also need to create and delete files by name. Communications: The first takes place between processes that are executing on the same computer; the second takes place between processes that are executing on different computer systems that are tied together by a computer network. Communications may be implemented via shared memory Error detection: The operating system constantly needs to be aware of possible errors. Errors may occur in the CPU and memory hardware (such as a memory error or a power failure), in I/O devices (such as a parity error on tape, a connection failure on a network, or lack of paper in the printer), and in the user program (such as an arithmetic overflow, an attempt to access an illegal memory location, or a too-great use of CPU time). For each type of error, the operating system should take the appropriate action to ensure correct and consistent computing. Resource allocation: When multiple users are logged on the system or multiple jobs are running at the same time, resources must be allocated to each of them. 9. When are real-time systems used? (NOVEMBER 2011) A real-time system is used when rigid time requirements have been placed on the operation of a processor or the flow of data. It is often used as a control device in a dedicated application.

4 10. Write the advantages of multiprogramming.(april/may 2012) Multiprogramming increases CPU utilization by organizing jobs so that the CPU always has one to execute. In a multiprogramming system, the operating system simply switches to, and executes, another job. As long as at least one job needs to execute, the CPU is never idle. e.g. A lawyer does not work for only one client at a time. While one case is waiting to go to trial or have papers typed, the lawyer can work on another case. 11. Write the advantage of distributed processing (APRIL 2013) Resource sharing Computation speedup Reliability Communication 12. What are system calls? (APRIL/MAY 2012) System calls provide the interface between a process and the operating system. These calls are generally available as assembly-language instructions, and they are usually listed in various manuals used by the assembly-language programmers. Certain systems allow system calls to be made directly from a higher level language program, in which case the calls normally resemble predefines function or subroutine calls. 13. Define information sharing (NOVEMBER 2012) Since several users may be interested in the same piece of information (for instance, a shared file), we must provide an environment to allow concurrent access to these types of resources. 14. What are the various states of process? (NOVEMBER 2012) As a process executes, it changes state. The state of a process is defined in part by the current activity of that process. Each process may be in one of the following states:

5 a. New: The process being created. b. Running: Instructions are being executed. c. Waiting: The process is waiting for some event to occur (such as an I/O completion or reception of a signal). d. Ready: The process is waiting to be assigned to a processor. e. Terminated: The process has finished execution. 15. What is a process control block? Each process is represented in the operating system by a process control block (PCB) also called a task control block. It contains many pieces of information associated with a specific process, including these: a. Process state b. Program counter c. CPU registers d. CPU-scheduling information. e. Memory-management information f. Accounting information. g. I/O status information 16. Give the reasons for suspend the process processing (APRIL 2013) Some of the reasons to suspend a process are. 1. If one process is ready to execute, but there is no space in the main memory, then it is suspended. 2. When one process in main memory which was blocked & there is another process ready to execute, but waiting in secondary memory, then the process in main memory is suspended. 3. When the parent process suspends, then the sub process is also suspended 17. What are the five major activities of an operating system in regard to process management? (APRIL/MAY 2014) Creating and deleting both user and system processes Suspending and resuming processes Providing mechanisms for process synchronization

6 Providing mechanisms for process communication Providing mechanisms for deadlock handling 18. Write notes on indirect communication. (NOVEMBER 2011) With indirect communication, the messages are sent to and receive from mailboxes, or ports. A mailbox can be viewed abstractly as an object into which messages can be placed by processes and from which messages can be removed. Each mailbox has a unique identification. In this scheme, a process can communicate with some other process via a number of different mailboxes. Two processes can communicate only if they share a mailbox. The send and receive primitives are defined as follows:a.send(a, message) Send a message to mailbox A.b.receive(A, message) Receive a message from mailbox A. 19. List out the benefits of OS. Cooperative process. (Nov/Dec 2016) 20. What is IPC? (Nov/Dec 2016) QUESTION BANK: 11 MARKS: 1. Write short notes on mainframe systems? (**) 2. Write short notes on clustered system?(***) 3. Explain distributed systems? (**) 4. Discuss the various operating system services? (****) 5. What are system calls and explain their types?(**) 6. Discuss about system programs(*) 7. Explain the concepts of I/O protection and memory protection.(5) 8. Explain the process state with a neat sketch. (6) 9. Describe the concept of cooperating processes and list their advantages. Also discuss the concept with producer consumer problem.

7 10. Discuss hardware protection with a neat diagram UNIT II Threads: Overview Threading issues - CPU Scheduling Basic Concepts Scheduling Criteria Scheduling Algorithms Multiple-Processor Scheduling Real Time Scheduling - The Critical- Section Problem Synchronization Hardware Semaphores Classic problems of Synchronization Critical regions Monitors. 1. What are the requirements that a solution to the critical section problem must satisfy?(april 2016) A solution to the critical-section problem must satisfy the following three requirements: Mutual Exclusion Progress Bounded Waiting 2. Compare user threads and kernel threads.( APRIL 2016) Threads may be provided at either the user level, for user threads, or by the kernel, for kernel threads. User Thread: User threads are supported above the kernel and are implemented by a thread library at the user level. The library provides support for thread creation, scheduling, and management with no support from the kernel. Kernal Thread: Kernel threads are supported directly by the operating system: The kernel performs thread creation, scheduling, and management in kernel space. Because thread management is done by the operating system, kernel threads are generally slower to create and manage than are user threads 3. What is meant by thread? (APRIL 2013)

8 A thread, sometimes called a lightweight process (LWP), is a basic unit of CPU utilization; it comprises a thread ID, a program counter, a register set, and a stack. It shares with other threads belonging to the same process its code section, data section, and other operating-system resources, such as open files and signals. 4. Difference between thread & process. (APRIL/MAY 2012) A thread, sometimes called a lightweight process (LWP), is a basic unit of CPU utilization; it comprises a thread ID, a program counter, a register set, and a stack. It shares with other threads belonging to the same process its code section, data section, and other operating-system resources, such as open files and signals. A process is a program in execution. A process is more than the program code, which is sometimes known as the text section. It also includes the current activity, as represented by the value of the program counter and the contents of the processor s registers. 5. Compare short term and long term scheduler (NOVEMEBER 2010) Whenever the CPU becomes idle, the operating system must select one of the processes in the ready queue to be executed. The selection process is carried out by the short-term-scheduler (or CPU scheduler).the long term scheduler, or job scheduler, selets processes from this pool and loads them into memory for execution. short-term-scheduler (or CPU scheduler), selects from among the processes that are ready to execute, and allocates the CPU to one of them. 6. What is semaphore? APRIL 2013 Semaphore is a synchronization tool that can resolve complex situation of critical section problems. A semaphore S is an integer variable that, apart from initialization, is accessed only through two standard atomic operations: wait and signal. These operations were originally termed P (for wait; from the Dutch proberen, to test) and V (for signal; from verhogen, to increment). The classical definition of wait in pseudocode is: wait(s) { while (S <= 0) ; // no-op

9 s--; } 7. What is monitor? (November 2016) Monitor are high-level synchronization construct. A monitor is characterized by a set of programmer-defined operators. The representation of a monitor type consists of declarations of variables whose values define the state of an instance of the type, as well as the bodies of procedures or functions that implement operations on the type. 8. List criterions used to evaluate the performance of cpu scheduling algorithms (NOVEMBER 2010) CPU utilization: We want to keep the CPU as busy as possible. CPU utilization may range from 0 to 100 percent. In a real system, it should range from 40 percent (for a lightly loaded system) to 90 percent (for a heavily used system). Throughput: If the CPU is busy executing processes, then work is being done.one measure of work is the number of processes completed per time unit, called throughput. For long processes, this rate may be 1 process per hour; for short transactions, throughput might be 10 processes per second. Turnaround time: The interval from the time of submission of a process to the time of completion is the turnaround time. Turnaround time is the sum of the periods spent waiting to get into memory, waiting in the ready queue, executing on the CPU, and doing I/O. Waiting time: Waiting time is the sum of the periods spent waiting in the ready queue. Response time: The measure of time from the submission of a request until the first response is produced. This measure, called response time, is the amount of time it takes to start responding, but not the time that it takes to output that response. The turnaround time is generally limited by the speed of the output device. 9. What is meant by race condition? APRIL/MAY 2014 A situation like this, 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 a race condition. To

10 guard against the race condition above, we need to ensure that only one process at a time can be manipulating the variable counter. To make such a guarantee, we require some form of synchronization of the processes 10. What is a dispatcher? (NOVEMBR 2011) The dispatcher is the module that gives control of the CPU to the process selected by the short-term-scheduler. This function involves: a. Switching context b. Switching to user mode c. Jumping to proper location in the user program to restart that program. 11. What is meant by dispatch latency? The time taken for the dispatcher to stop one process and start another running is known as dispatch latency. 12. List the various scheduling criterions. The scheduling criterions include the following: a. CPU utilization b. Throughput c. Turnaround time d. Waiting time e. Response time. 13. Define throughput. (NOVEMBR 2011) The number of processes completed per time unit is called throughput. 14. Define turnaround time. (NOVEMBR 2012) The interval from the time of submission of a process to the time of completion is the turnaround time. 15. Define waiting time. Waiting time is the sum of the periods spent waiting in the ready queue. 16. Define response time.

11 Response time is the amount of time it takes to starts responding. 17. Name some CPU scheduling algorithms. Some of the CPU scheduling algorithms are as follows: a. First-Come, First-Served scheduling b. Shortest-Job-First scheduling c. Priority scheduling d. Round-Robin scheduling e. Multilevel queue scheduling 18. What is meant priority inversion? The high-priority process would be waiting for a lower-priority one to finish. A chain of processes could all be accessing resources that the high-priority process needs. Consider a system consisting of n processes {Po,P1,..., P,-1). Each process has a segment of code, called a critical section, in which the process may be changing common variables, updating a table, writing a file, and so on. The important feature of the system is that, when one process is executing in its critical section, no other process is to be allowed to execute in its critical section. Thus, the execution of critical sections by the processes is mutually exclusive in time. Each process must request permission to enter its critical section. The section of code implementing this request is the entry section. The critical section may be followed by an exit section. The remaining code is the remainder section. 19. What is aging? Aging is a technique of gradually increasing the priority of processes that wait in the system for along time. 20. Which scheduling does time-sharing systems use? Explain. The Round-Robin (RR) scheduling algorithm is designed especially for time-sharing systems. It is similar to FCFS scheduling, but preemption is added to switch between processes. A small unit of time, called a time quantum (or time slice), is defined. A time quantum is generally from 10 to 100 milliseconds. The

12 ready queue is treated as a circular queue. The CPU scheduler goes around the ready queue, allocating the CPU to each process for a time interval of up to 1 time quantum. 21. Which scheduling policy is most suitable for a timeshared operating system? (APRIL/MAY 2012) Round robin scheduling: Scheduling policy that permits each ready process to execute for at most one quantum per round. After the last process in the queue has executed once, the scheduler begins a new round by scheduling the first process in the queue. 22. What is asymmetric multiprocessing? (NOVEMBER 2012) Asymmetric multiprocessing, (AMP) in which each processor is assigned a specific task. A master processor controls the system; the other processors either look to the master for instruction or have predefined tasks. This scheme defines a master-slave relationship. The master processor schedules and allocates work to the slave processors. 23.Define Race Condition. (Nov/Dec 2016) 24. Name the requirements that a solution to the critical section problem must satisfy. (Nov/Dec 2016) QUESTION BANK 11 MARKS 1. Write notes on schedulers? ** (8) 2. What are the criteria used for comparing CPU scheduling algorithm? * (11) 3. Explain briefly about FCFS? * (6) 4. Explain preemptive scheduling briefly? ** (11) 5. Explain how multiprocessor scheduling differs from real- time scheduling? * (8) 6. Discuss any two pre-emptive process scheduling algorithm? * (11) 7. Explain priority scheduling with example? * (8) 8. Explain round robin scheduling with example? *** (8) 9. Explain how multiprocessor scheduling? * (7) 10. Discuss the critical section problems with suitable example? *** (11)

13 11. Explain synchronization hardware? * (8) 12. Explain Semaphores and its implementation. (**) (11) 13. Explain about the Classic Problems of Synchronization.(*) 14. Explain the dining philosopher concepts? (**) (7) 15. What are Monitors? Explain in detail. (*) (11) 16. Explain how dining philosopher problem can be solved by Monitors (8) 17. Explain the Possible implementation of the monitor mechanism using semaphores? (7) 18. What are the criteria for scheduling? (5) 19. Calculate average waiting time and average turnaround time for the following algorithms. (a) FCFS (b) Preemptive SJF (SRTF) (c) Round robin (quantum = 1ms) Process Arrival Time Burst Time P1 0 7 P2 1 3 P3 2 8 P4 3 5

14 UNIT III System Model: Deadlock Characterization Methods for handling Deadlocks Deadlock Prevention Deadlock avoidance Deadlock detection Recovery from Deadlocks Storage Management Swapping Contiguous Memory allocation Paging Segmentation Segmentation with Paging. 1. What are the four necessary conditions to occur deadlock? (NOVEMBER 2010). APRIL/MAY 2014 Mutual exclusion: At least one resource must be held in a non sharable mode; that is, only one process at a time can use the resource. If another process requests that resource, the requesting process must be delayed until the resource has been released. Hold and wait: A process must be holding at least one resource and waiting to acquire additional resources that are currently being held by other processes. No preemption: Resources cannot be preempted; that is, a resource can be released only voluntarily by the process holding it, after that process has completed its task. Circular wait: A set {Po, PI,..., Pn,) of waiting processes must exist such that Po is waiting for a resource that is held by PI, PI is waiting for a resource that is held by P2,..., P3, Pl is waiting for a resource that is held by Pn,, and Pn, is waiting for a resource that is held by Po. 2. Define swapping. (APRIL 2016) A process need to be in memory to be executed. A process, can be swapped temporarily out of memory to a backing store, and then brought back into memory for continued execution. This technique is known as swapping. 3. What is resource allocation graph? NOVEMBER 2011, APRIL/MAY 2012,2016

15 A claim edge Pi -> Rj indicates that process Pi may request resource Rj at some time in the future. This edge resembles a request edge in direction, but is represented by a dashed line. When process Pi requests resource Rj, the claim edge Pi -> Rj is converted to a request edge. Similarly, when a resource Rj is released by Pi,th e assignment edge Rj -> Pi is reconverted to a claim edge Pi ->Xi. (i.e) the resources must be claimed a prior in the system. That is, before process Pi starts executing, all its claim edges must already appear in the resource-allocation graph. Suppose that process Pi requests resource Rj. The request can be granted only if converting the request edge Pi -> Rj to an assignment edge Rj -> Pi does not result in the formation of a cycle in the resource-allocation graph. If no cycle exists, then the allocation of the resource will leave the system in a safe state. If a cycle is found, then the allocation will put the system in an unsafe state. Therefore, process Pi will have to wait for its requests to be satisfied. 4. List the two techniques that enhance performance creating and running processes.(november 2015) Two techniques made available by virtual memory that enhance performance creating and running processes. a) copy-on-write b) Memory mapped files 5. When is a system in a safe state? (APRIL 2013) The resources must be claimed a prior in the system. That is, before process Pi starts executing, all its claim edges must already appear in the resource-allocation graph. Suppose that process Pi requests resource Rj. The request can be granted only if converting the request edge Pi -> Rj to an assignment edge Rj -> Pi does not result in the formation of a cycle in the

16 resource-allocation graph. If no cycle exists, then the allocation of the resource will leave the system in a safe state. 6. What is the use of overlays? (NOVEMBER 2010) To enable a process to be larger than the amount of memory allocated to it, overlays can be used. The idea of overlays is to keep in memory only those instructions and data that are needed at any given time. 7. Explain paging technique. APRIL/MAY 2014 Paging is a memory-management scheme that permits the physical-address space of a process to be noncontiguous. Paging avoids considerable problem of fitting the varying-sized memory chunks onto the backing store, from which most of the previous memory-management schemes suffered. 8. What is the use of page table (NOVEMBER 2012) Every address generated by the CPU is divided into two parts: a page number (p) and a page offset (d). The page number is used as an index into a page table. The page table contains the base address of each page in physical memory. This base address is combined with the page offset to define the physical memory address that is sent to the memory unit. 9. Explain segmentation. (NOVEMBER 2012) The logical-address space is a collection of segments. The process of mapping the logical address space to the physical address space using a segment table is known as segmentation. 10. With segmentation, if there are 64 segments & maximum segment size in 512 words then what is the length of logical address? APRIL 2013 To specify a particular segment, 64 bits are required (since 2^6=64) Having selected a page, to select a particular byte one needs 9 bits (since 2^9=512(1k byte=1024bits). So totally 6+9=15 bits are needed.

17 11. What are the criteria for CPU page replacement algorithm? (APRIL/MAY 2012) 1. Find the location of the desired page on the disk. 2. Find a free frame: a. If there is a free frame, use it. b. If there is no free frame, use a page-replacement algorithm to select a victim frame. c. Write the victim page to the disk; change the page and frame tables accordingly. 3. Read the desired page into the (newly) free frame; change the page and frame tables. 4. Restart the user process. 12. What is a memory-management unit? The run-time mapping from virtual to physical address is done by a hardware device called the memory-management unit. 13. Write short notes on dynamic loading. To obtain better memory-space utilization, dynamic loading can be used. A routine is not loaded until it is called. The advantage of dynamic loading is that an unused routine is never loaded. This method is particularly useful when large amount of code are needed to handle infrequently occurring cases, such as error routines. 14. Write notes on contiguous storage allocation. The memory is usually divided into two partitions: one for resident operating system, and one for the user processes. The operating system may be placed in either low or high memory. The major factor affecting this decision is the location of interrupt vector. Since the interrupt vector is often in low memory, programmers usually place the operating system in low memory as well. In this contiguous memory allocation, each process is contained in a single contiguous section of memory.

18 15. What is internal fragmentation? Memory that is internal to a partition but is not being used results in internal fragmentation. 16. Explain roll out, roll in. If a higher-priority process arrived and wants service, the memory manager can swap out the lower-priority process so that it can load and execute the higherpriority process. When the higher-priority process finishes, the lower-priority process can be swapped back in and continued. This variant of swapping is sometimes called roll out, rollin. 17. It is possible to have deadlock involving only one process? Explain.(Nov/Dec 2016) 18. List out the uses of shared pages. (Nov/Dec 2016) QUESTION BANK 11 MARKS 1. Explain necessary conditions to avoid deadlock? (*) 2. Explain the construction of resource allocation graph? (**) 3. Explain the characteristics of deadlock? (*) 4. Discuss the dynamic loading & linking program during execution? (*) 5. Define overlay. How it differs from swapping? * (*) 6. Explain contiguous memory allocation method highlighting its advantage? *** (11) 7. Define external fragmentation. How can it be avoided? * (8) 8. Explain the difference between external & internal fragmentation? (5) * 9. Explain various techniques for structuring the page table. (7) ** 10. Expalin the schematic diagram of paging? (11) **

19 11. Differentiate paging and segmentation? (11) **** 12. What is the need of segmentation paging? Exaplin the same? ** (11) 13. How segmentation differ from paging? What is the role of memory management unit in the process of segmentation? ** (8) UNIT IV Virtual Memory Demand Paging Process creation Page Replacement Allocation of frames Thrashing. File Concept: Access Methods Directory Structure File System Mounting File Sharing Protection. 1. What is a meant by thrashing? (NOVEMBER 2010) The process is brought in and taken out of the memory and is not allowed to execute. This technique is known as thrashing. 2. Mention about external fragmentation? APRIL/MAY 2014 External fragmentation A B A C B C (a) One contiguous memory block allocated by A,B,C It is the phenomenon in which free storage become divided into many small pieces over time. It occurs when an application allocates & deallocates regions of storage of varying sizes & the allocation algorithm responds by leaving the allocated & de-allocated regions interspersed. The result in that although free space is available it is effectively unusable because it is divided into pieces that are too small to satisfy the demands of the application. A A C C C request free memory but it isn t contiguous & remain unused

20 One solution to the problem of external fragmentation is compaction. The goal is to shuffle the memory contents to place all free memory together in one large block. 3. What are the types of file access methods? NOVEMEBER 2010 Sequential Access:The simplest access method is sequential access. Information in the file is processed in order, one record after the other. This mode of access is by far the most common; for example, editors and compilers usually access files in this fashion.the bulk of the operations on a file is reads and writes. Another method is direct access (or relative access). A file is made up of fixed length logical records that allow programs to read and write records rapidly in no particular order.the direct-access method is based on a disk model of a file, since disks allow random access to any file block. For direct access, the file is viewed as a numbered sequence of blocks or records. Other access methods can be built on top of a direct-access method. These methods generally involve the construction of an index for the file. The index, like an index in the back of a book, contains pointers to the various blocks. To find a record in the file, we first search the index, and then use the pointer to access the file directly and to find the desired record. 4. List the methods used to manage the free spaces. NOVEMEBER 2010 To keep track of free disk space, the system maintains a free-space list. create a file, we search the free-space list for the required amount of space, and allocate that space to the new file. This space is then removed from the free-space list. When a file is deleted, its disk space is added to the freespace list. The free-space list, despite its name, might not be implemented as a list, as we shall discuss. Bit Vector: Frequently, the free-space list is implemented as a bit map or bit vector. Each block is represented by 1 bit. If the block is free, the bit is 1; if the block is allocated, the bit is 0. Linked List: Another approach to free-space management is to link together all the free disk blocks, keeping a pointer to the first free block in a special location on the disk and caching it in memory. This first block contains a pointer to the next free disk block, and so on.

21 Grouping: rather than keeping a list of n free disk addresses, we can keep the address of the first free block and the number n of free contiguous blocks that follow the first block. Each entry in the free-space list then consists of a disk address and a count. 5. List out the file attributes NOVEMBR 2011, NOVEMBER 2012 Name: The symbolic file name is the only information kept in human readable form. Identifier: This unique tag, usually a number, identifies the file within the file system; it is the non-human-readable name for the file. Type: This information is needed for those systems that support different types. Location: This information is a pointer to a device and to the location of the file on that device. Size: The current size of the file (in bytes, words, or blocks), and possibly the maximum allowed size are included in this attribute. Protection: Access-control information determines who can do reading, writing, executing, and so on. Time, date, and user identification: This information may be kept for creation, last modification, and last use. These data can be useful for protection, security, and usage monitoring. 6. What you mean by seek time? APRIL/MAY 2012 The seek time is the time for the disk arm to move the heads to the cylinder containing the desired sector. 7. Give any two criteria to choose a file organization APRIL/MAY 2012 In choosing a file organization, several criteria are important: a. Short access time b. Ease of update c. Economy of storage d. Simple maintenance e. Reliability

22 8. List the disk performance parameters APRIL 2013 Speed Reliability Cost 9. What is the purpose of devices? APRIL 2013 A contrivance or an invention serving a particular purpose, especially a machine used to perform one or more relatively simple tasks. A technique or means. 10. Define bootstrap program (NOVEMBER 2012) When a computer is powered up or rebooted- it needs to have an initial program to run. That program is bootstrap program. It is stored in ROM or EEPROM within computer Hardware. Bootstrap program must know how to load the OS and to start executing that system. 11. What is a process? A process is a program in execution. A process is more than the program code, which is sometimes known as the text section. It also includes the current activity, as represented by the value of the program counter and the contents of the processor s registers. 12. How does FIFO page replacement work? A FIFO page replacement algorithm associates with each page the time when that page was brought into memory. When a page must be replaced, the oldest page is chosen. 13. State Belady s anomaly Belady s anomaly states that for some page replacement algorithms, the page-fault rate may increase as the number of allocated frames increases. 14. Explain lease-recently-used algorithm.

23 LRU replacement associates with each page the time of that page s last use. When a page must be replaced, LRU chooses that page that has not been used for the longest period of time. 15. Describe least frequently used page-replacement. The least frequently used (LFU) page-replacement algorithm requires that the page with the smallest count be replaced. 16. How does most frequently used page-replacement work? The most frequently used (MFU) page-replacement algorithm is based on the argument that the page with the smallest count was probably just brought in and has yet to be used. QUESTION BANK 11 MARKS 17.Name the various layers of file system. (Nov/Dec 2016) 18.What are the advantages of contiguous allocation? (Nov/Dec 2016) 1. Explain with diagram of swapping two processes using a backing store? * (8) 2. Explain about allocation of Frames 3. Explain Thrashing. ** 4. Explain about Allocation Algorithms. (6) 5. What is page replacement? Explain how it will be done in the memory? 6. (a) What is thrashing? Explain. (4) (b) Explain the different file access methods. (7) 7. Elucidate FIFO, Optimal and LRU page replacement techniques for the following 2, 3, 2, 1, 5, 2, 4, 5, 3, 2, 5, 2 8. Explain about various directory structures. 9. Elucidate FIFO, Optimal and LRU page replacement techniques for the following 2, 3, 2, 1, 5, 2, 4, 5, 3, 2, 5, 2

24 UNIT-V File System Structure File System Implementation Directory Implementation Allocation Methods Free-space Management. Kernel I/O Subsystems - Disk Structure Disk Scheduling Disk Management Swap-Space Management. Case Study: The Linux System, Windows. 1. What are the functions of virtual file system (VFS)? (APRIL 2016) (i) It separates file-system-generic operations from their implementation by defining a clean VFS interface. Several implementations for the VFS interface may coexist on the same machine, allowing transparent access to different types of file systems mounted locally. (ii) The VFS is based on a file-representation structure, called a v- node, that contains a numerical designator for a network-wide unique file. (UNIX inodes are unique within only a single file system.) This networkwide uniqueness is required for support of network file systems. The kernel maintains one v-node structure for each active node (file or directory). Thus, the VFS distinguishes local files from remote ones, and local files are further distinguished according to their file-system types.

25 2. What is FCB? NOVEMEBER 2010, APRIL/MAY 2014 An FCB contains many of the file's details, including file permissions, ownership, size, and location of the data blocks. In UFS this is called the inode. In NTFS, this information is actually stored within the Master File Table, which uses a relational database structure, with a row per file. The structures can include: The system-wide open-file table contains a copy of the FCB of each open file, as well as other information. The per-process open-file table contains a pointer to the appropriate entry in the system-wide open-file table, as well as other information. To create a new file, an application program calls the logical file system. The logical file system knows the format of the directory structures. To create a new file, it allocates a new FCB, reads the appropriate directory into memory, updates it with the new file name and FCB, and writes it back to the disk. A typical FCB is shown in Figure (b). Figure (b): Typical File control Block 3. How does windows handle inter process communication? NOV 15 Windows XP provides many interprocess communication (IPC) mechanisms to allow processes to exchange data and cooperate to complete tasks. It implements many traditional UNIX IPC mechanisms, such as pipes, message queues (called mailslots by Windows XP) and shared memory. In addition to these data-oriented IPCs, windows XP allows processes to communicate through procedure-oriented or Object-oriented techniques, using such tools as remote procedure calls or Microsoft s Component Object Model. 4. Define kernel is operating system? APRIL/MAY 2012/NOV 15

26 An OS is a software that enables application to interact with a computers hardware. The software that contains the core components of the OS is called kernel. The kernel is the essential center of a computer operating system, the core that provides basic services for all other parts of the operating system. A synonym is nucleus. A kernel can be contrasted with a shell, the outermost part of an operating system that interacts with user commands. Kernel and shell are terms used more frequently in Unix operating systems than in IBM mainframe or Microsoft Windows systems. 5. Write the three levels of page tables in Linux systems APRIL/MAY 2014 The virtual memory system supports up to three levels of page tables to locate the mapping between virtual pages and page frames. The first level of the page table hierarchy called the page global directory, stores addresses of second level tables. Second level tables called page middle directories, store addresses of the third level tables. The third level, simply called page tables, maps virtual pages to page frames. 6. What is meant by prefetching? APRIL/MAY 2014 Feature introduced in Microsoft windows XP that enables windows to load portions of commonly run programs, when the computer first loads, enabling frequently run programs to load faster. 7. What are the ways available to display the contents of a folder window? APRIL 2013 Using Folder Options in Control Panel, you can change the way your files and folders function, as well as how the content in your folders is displayed. Open Folder Options by clicking the Start button, clicking Control Panel, clicking Appearance and Personalization, and then clicking Folder Options. 8. List the protocols that can transmit IP communications across the telephone lines. APRIL 2013

27 The Session Initiation Protocol (SIP) is a signaling communications protocol, widely used for controlling multimedia communication sessions such as voice and video calls over Internet Protocol (IP) networks. The protocol defines the messages that are sent between endpoints which govern establishment, termination and other essential elements of a call. SIP can be used for creating, modifying and terminating sessions consisting of one or several media streams. SIP can be used for two-party (unicast) or multiparty (multicast) sessions. Other SIP applications include video conferencing, streaming multimedia distribution, instant messaging, presence information, file transfer, fax over IP and online games. 9. Define bootstrap program (NOVEMBER 2012) When a computer is powered up or rebooted- it needs to have an intial program to run. That program is bootstrap program. It is stored in ROM or EEPROM within computer Hardware. Bootstrap program mus know how to load the o.s and to start executing that system. 10. Write any two advantages in Linux? NOVEMBR 2011, NOVEMBER 2012 TOPIC LINUX Reliability The majority of Linux variants and versions are notoriously reliable and can often run for months and years without needing to be rebooted. Software Linux has a large variety of available software programs, utilities, and games. However, Windows has a much larger selection of available software. Software Cost Many of the available software programs, utilities, and games available on Linux are freeware or open source. Even such complex programs such as Gimp, OpenOffice, StarOffice, and wine are available for free or at a low cost. Hardware Although hardware manufacturers have made great advancements in supporting Linux it still will not support most hardware devices. However, for the hardware devices that have driver support they will usually work in all versions of Linux.

28 Security Open Source Support Linux is and has always been a very secure operating system. Although it still can be attacked when compared to Windows, it much more secure. Many of the Linux variants and many Linux programs are open source and enable users to customize or modify the code however they want to. Although it may be more difficult to find users familiar with all Linux variants, there are vast amounts of available online documentation and help, available books, and support available for Linux. 11. What are security methods in windows XP? (NOV 11, NOV 15) Window XP provides users with a range of authentication and authorization options that permit access a physical terminal, a local network or the internet. A database of users credentials helps provide users with single signon; once a user log on to windows XP, the system take care of authenticating the user to other domains and networks without prompting for credentials. The operating system includes a build- in firewall that protects the system from malicious access. 12. Sketch the components of LINUX system. (NOV 14) System management programs User utility programs Linux Kernel Loadable kernel modules System shared libraries 13. What is PC? APRIL/MAY 2012 A personal computer (PC) is a general-purpose computer, whose size, capabilities and original sale price makes it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator. This contrasted with the batch processing or time-

29 sharing models which allowed larger, more expensive minicomputer and mainframe systems to be used by many people, usually at the same time. Large data processing systems require a full-time staff to operate efficiently. 14. What is the use of registry in windows XP? Who is responsible to manage it?(apr 12) Windows XP use the registry to store and access data in centralized manner. For example, when user installs a hard ware device, device drivers place configuration information in to the registry. The configuration manager is the executive component responsible for managing the registry. 15. What do you mean by porting?(apr 12) The code that performs operation that is implemented differently across architecture is called architecture specific code. The process of modifying the kernel to support new architecture is called porting. 16. What is the use of boot block A boot control block can contain information needed by the system to boot an operating from that partition. If the disk does not contain an operating system, this block can be empty. It is typically the first block of a partition. In UFS, this is called the boot block; in NTFS, it is the partition boot sector. 17. What are the basic principles of UNIX process management?(nov 15) The process management subsystem is essential to providing efficient multiprogramming in Linux. Although responsible primarily for allocating processors to processes, the process management subsystem also delivers signals, loads kernel modules and receives interrupts the process management subsystem contains the process scheduler, which provides processes access to a processor in a reasonable amount of time. 18. List out the different components of Linux system. (Nov/Dec 2016)

30 19. What are the security mechanisms available in windows XP? (Nov/Dec 2016) 11 MARKS 1. Elaborate on the various allocation methods in a file system.(nov15) 2. Explain the concepts and functions of inter process communication and synchronization in Linux and window XP operating systems.(nov15) 3. Explain the activities and functionalities of memory and file management in windows XP. 4. Enumerate file allocation methods with example. (MAY 16) 5. Discuss about: (a) Disk management (5) (b) Swap space management (6) (MAY 16) 6. Describe briefly about disk scheduling. (NOV 15) 7. Discuss on file system structure in the linux system. (NOV 15) 8. Explain about the inter process communication? 9. Explain about memory management in Linux. 10. Explain about different linux hardware platforms. 11. Explain about Linux system architecture. (NOV 11) 12. Explain about system management mechanism. (NOV 11) 13. Explain process management in linux systems. 14. Explain how the inter process communication is carried out in linux OS. (APR13) 15. Explain how the memory & file management is implemented in window XP. (APR13) 16. Write about the process management in Linux.(NOV 10) 17. A hard disk having 500 cylinders, numbered from 0 to 499. The head starts at cylinder 120. (NOV 10) The status of the queue is as follows: 86, 13, 127, 150, 132, 175, 130, 428 What is total distance (in cylinders) that the disk arm moves to satisfy the entire pending request for each of the following disk scheduling algorithms a) SSTF b) FCFS c) SCAN

31 d) LOOK e) C-SCAN f) C-LOOK 18. (a). compare and contrast the various issues in security related to Linux and Windows XP operating systems.(5) (b). state and explain the ways in which an applications uses memory in windows. (6)