Operating System

OPERATING SYSTEM

PARTA
1. What is an Operating system?
             An operating system is a program that manages the computer
      hardware. It also provides a basis for application programs and
      act as an intermediary between a user of a computer and the
      computer hardware. It controls and coordinates the use of the
      hardware among the various application programs for the various
      users.
2. Why is the Operating System viewed as a resource allocator & control
   program?
             A computer system has many resources hardware & software
      that may be required to solve a problem, like CPU time, memory
      space, filestorage space, I/O devices & so on. The OS acts as a
      manager for these resources so it is viewed as a resource
      allocator.The OS is viewed as a control program because it
      manages the execution of user programs to prevent errors &
      improper use of the computer.
3. What is the Kernel?
             A more common definition is that the OS is the one program
      running at all times on the computer, usually called the kernel,
      with all else being application programs.
4. What are Batch systems?
             Batch systems are quite appropriate for executing large
      jobs that need little interaction. The user can submit jobs and
      return later for the results. It is not necessary to wait while
      the job is processed. Operators batched together jobs with
      similar needs and ran them through the computer as a group.
5. What is the advantage of Multiprogramming?
             Multiprogramming increases CPU utilization by organizing
      jobs so that the CPU always has one to execute. Several jobs are
      placed in the main memory and the processor is switched from job
      to job as needed to keep several jobs advancing while keeping the
      peripheral devices in use. Multiprogramming is the first instance
      where the Operating system must make decisions for the users.
      Therefore they are fairly sophisticated.
6. What is an Interactive computer system?
             Interactive computer system provides direct communication
      between the user and the system. The user gives instructions to
      the operating system or to a program directly, using a keyboard
      or mouse ,and waits for immediate results.
7. What do you mean by Timesharing systems?
             Timesharing or multitasking is a logical extension of
      multiprogramming. It allows many users to share the computer
      simultaneously. The CPU executes multiple jobs by switching among

them, but the switches occur so frequently that the users can
      interact with each program while it is running.
8. What are multiprocessor systems & give their advantages?
            Multiprocessor systems also known as parallel systems or
      tightly coupled systems are systems that have more than one
      processor in close communication, sharing the computer bus, the
      clock and sometimes memory & peripheral devices. Their main
      advantages are
• Increased throughput
• Economy of scale
• Increased reliability
9. What are the different types of multiprocessing?
            Symmetric multiprocessing (SMP): In SMP each processor runs
      an identical copy of the Os & these copies communicate with one
      another as needed. All processors are peers. Examples are Windows
      NT, Solaris, Digital UNIX, OS/2 & Linux.
            Asymmetric multiprocessing: Each processor is assigned a
      specific task. A master processor controls the system; the other
      processors look to the master for instructions or predefined
      tasks. It defines a masterslave relationship. Example SunOS
      Version 4.
10.What is graceful degradation?
            In multiprocessor systems, failure of one processor will
      not halt the system, but only slow it down. If there are ten
      processors & if one fails the remaining nine processors pick up
      the work of the failed processor. This ability to continue
      providing service is proportional to the surviving hardware is
      called graceful degradation.
11.What is DualMode Operation?
            The dual mode operation provides us with the means for
      protecting the operating system from wrong users and wrong users
      from one another. User mode and monitor mode are the two modes.
      Monitor mode is also called supervisor mode, system mode or
      privileged mode. Mode bit is attached to the hardware of the
      computer to indicate the current mode. Mode bit is '0' for
      monitor mode and '1' for user mode.
12.What are privileged instructions?
            Some of the machine instructions that may cause harm to a
      system are designated as privileged instructions. The hardware
      allows the privileged instructions to be executed only in monitor
      mode.
13.How can a user program disrupt the normal operations of a system?
            A user program may disrupt the normal operation of a system
      by
      • Issuing illegal I/O operations
      • By accessing memory locations within the OS itself

• Refusing to relinquish the CPU
14.How is the protection for memory provided?
            The protection against illegal memory access is done by
      using two registers. The base register and the limit register.
      The base register holds the smallest legal physical address; the
      limit register contains the size of the range. The base and limit
      registers can be loaded only by the OS using special privileged
      instructions.
15.What are the various OS components?
      The various system components are
            • Process management
            • Mainmemory management
            • File management
            • I/Osystem management
            • Secondarystorage management
            • Networking
            • Protection system
            • Commandinterpreter system
16.What is a process?
            A process is a program in execution. It is the unit of work
      in a modern operating system. A process is an active entity with
      a program counter specifying the next instructions to execute and
      a set of associated resources. It also includes the process
      stack, containing temporary data and a data section containing
      global variables.
17.What is a process state and mention the various states of a process?
            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:
      • New
      • Running
      • Waiting
      • Ready
      • Terminated
18.What is process control block?
            Each process is represented in the operating system by a
      process control block also called a task control block. It
      contains many pieces of information associated with a specific
      process. It simply acts as a repository for any information that
      may vary from process to process. It contains the following
      information:
      • Process state
      • Program counter
      • CPU registers
      • CPUscheduling information
      • Memorymanagement information

• Accounting information
      • I/O status information
19.What are the use of job queues, ready queues & device queues?
            As a process enters a     system, they are put into a job
      queue. This queue consists     of all jobs in the system. The
      processes that are residing     in main memory and are ready &
      waiting to execute are kept   on a list called ready queue. The
      list of processes waiting for  a particular I/O device is kept in
      the device queue.
20.What is meant by 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 context switch. The context of a
      process is represented in the PCB of a process.
21.What is a thread?
            A thread otherwise called a lightweight process (LWP) is a
      basic unit of CPU utilization, it comprises of 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 operating system resources such as open files and
      signals.
22.What are the benefits of multithreaded programming?
            The benefits of multithreaded     programming  can  be   broken
      down into four major categories:
      • Responsiveness
      • Resource sharing
      • Economy
      • Utilization of multiprocessor architectures
23.Compare user threads and kernel threads.
            User threads
                  User threads are supported above the kernel and are
            implemented by a thread library at the user level. Thread
            creation & scheduling are done in the user space, without
            kernel intervention. Therefore they are fast to create and
            manage blocking system call will cause the entire process
            to block
            Kernel threads
                  Kernel   threads  are    supported   directly    by   the
            operating system .Thread creation, scheduling and
      management are done by the operating system. Therefore they are
      slower to create & manage compared to user threads. If the thread
      performs a blocking system call, the kernel can schedule
      another thread in the application for execution
24.What is the use of fork and exec system calls?
            Fork is a system call by which a new process is created.
      Exec is also a system call, which is used after a fork by one of

the two processes to replace the process memory space with a new
      program.
25.Define thread cancellation & target thread.
            The thread cancellation is the task of terminating a thread
      before it has completed. A thread that is to be cancelled is
      often referred to as the target thread.
            For example, if multiple threads are concurrently searching
      through a database and one thread returns the result, the
      remaining threads might be cancelled.
26.What are the different ways in which a thread can be cancelled?
            Cancellation of a target thread may occur in two different
      scenarios:
            •   Asynchronous   cancellation:   One  thread    immediately
      terminates the target thread is called asynchronous cancellation.
            • Deferred cancellation: The target thread can periodically
      check if it should terminate, allowing the target thread an
      opportunity to terminate itself in an orderly fashion.
27.Define CPU scheduling.
            CPU scheduling is the process of switching the CPU among
      various processes. CPU scheduling is the basis of multiprogrammed
      operating systems. By switching the CPU among processes, the
      operating system can make the computer more productive.
28.What is preemptive and nonpreemptive scheduling?
            Under nonpreemptive scheduling once the CPU has been
      allocated to a process, the process keeps the CPU until it
      releases the CPU either by terminating or switching to the
      waiting state. Preemptive scheduling can preempt a process which
      is utilizing the CPU in between its execution and give the CPU to
      another process.
29.What is a Dispatcher?
            The dispatcher is the module that gives control of the CPU
      to the process selected by the shortterm scheduler. This
      function involves:
      • Switching context
      • Switching to user mode
      • Jumping to the proper location in the user program to restart
        that program.
30.What is dispatch latency?
            The time taken by the dispatcher to stop one process and
      start another running is known as dispatch latency.
31.What are the various scheduling criteria for CPU scheduling?
            The various scheduling criteria are
      • CPU utilization
      • Throughput
      • Turnaround time
      • Waiting time

• Response time
32.Define throughput?
            Throughput in CPU scheduling is the number of processes
      that are completed per unit time. For long processes, this rate
      may be one process per hour; for short transactions, throughput
      might be 10 processes per second.
33.What is turnaround time?
            Turnaround time is the interval from the time of submission
      to the time of completion of a process. It 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.
34.Define race condition.
            When several process access and manipulate same data
      concurrently, then the outcome of the execution depends on
      particular order in which the access takes place is called race
      condition. To avoid race condition, only one process at a time
      can manipulate the shared variable.
35.What is critical section problem?
            Consider a system consists of 'n' processes. Each process
      has segment of code called a critical section, in which the
      process may be changing common variables, updating a table,
      writing a file. When one process is executing in its critical
      section, no other process can allowed to execute in its critical
      section.
36.What are the requirements that a solution to the critical section
problem must satisfy?
            The three requirements are
      • Mutual exclusion
      • Progress
      • Bounded waiting
37.Define entry section and exit section.
             The critical section problem is to design a protocol that
      the processes can use to cooperate. Each process must request
      permission to enter its critical section. The section of the code
      implementing this request is the entry section. The critical
      section is followed by an exit section. The remaining code is the
      remainder section.
38.Give two hardware instructions and their definitions which can be
used for implementing mutual exclusion.
      • TestAndSet
             boolean TestAndSet (boolean &target)
             {
                   boolean rv = target;
                   target = true;
                   return rv;
             }

• Swap
             void Swap (boolean &a, boolean &b)
             {
                   boolean temp = a;
                   a = b;
                   b = temp;
             }
39.What is semaphores?
             A semaphore 'S' is a synchronization tool which is an
      integer value that, apart from initialization, is accessed only
      through two standard atomic operations; wait and signal.
      Semaphores can be used to deal with the nprocess critical
      section problem. It can be also used to solve various
      synchronization problems. The classic definition of 'wait'
             wait (S)
             {
                   while (S<=0)
                   ;
                          S;
             }
             The classic definition of 'signal'
             signal (S)
             {
                   S++;
             }
40.Define busy waiting and spinlock.
            When a process is in its critical section, any other
      process that tries to enter its critical section must loop
      continuously in the entry code. This is called as busy
      waiting and this type of semaphore is also called a spinlock,
      because the process while waiting for the lock.
41.Define deadlock.
            A process requests resources; if the resources are not
      available at that time, the process enters a wait state. Waiting
      processes may never again change state, because the resources
      they have requested are held by other waiting processes. This
      situation is called a deadlock.
42.What is the sequence in which resources may be utilized?
            Under normal mode of operation, a process may utilize a
      resource in the following sequence:
            • Request: If the request cannot be granted immediately,
      then the requesting process must wait until it can acquire the
      resource.
      • Use: The process can operate on the resource.
      • Release: The process releases the resource.
43.What are conditions under which a deadlock situation may arise?

A deadlock situation can arise if       the  following four
      conditions hold simultaneously in a system:
            a. Mutual exclusion
            b. Hold and wait
            c. No preemption
44.What is a resourceallocation graph?
            Deadlocks can be described more precisely in terms of a
      directed graph called a system resource allocation graph. This
      graph consists of a set of vertices V and a set of edges E. The
      set of vertices V is partitioned into two different types of
      nodes; P the set consisting of all active processes in the
      system and R the set consisting of all resource types in the
      system.
45.Define request edge and assignment edge.
            A directed edge from process Pi to resource type Rj is
      denoted by PiàRj; it signifies that process Pi requested an
      instance of resource type Rj and is currently waiting for that
      resource. A directed edge from resource type Rj to process Pi is
      denoted by RjàPi, it signifies that an instance of resource type
      has been allocated to a process Pi. A directed edge PiàRj is
      called a request    edge.  A  directed  edge  RjàPi is  called an
      assignment edge.
46.What are the methods for handling deadlocks?
            The deadlock problem can be dealt with in one of the three
      ways:
      a. Use a protocol to prevent or avoid deadlocks, ensuring that
      the system will never enter a deadlock state.
      b. Allow the system to enter the deadlock state, detect it and
      then recover.
      c. Ignore the problem all together, and pretend that deadlocks
         never occur in the system.
47.Define deadlock prevention.
            Deadlock prevention is a set of methods for ensuring that
      at least one of the four necessary conditions like mutual
      exclusion, hold and wait, no preemption and circular wait cannot
      hold. By ensuring that that at least one of these conditions
      cannot hold, the occurrence of a deadlock can be prevented.
48.Define deadlock avoidance.
            An alternative method for avoiding deadlocks is to require
      additional information about how resources are to be requested.
      Each request requires the system consider the resources currently
      available, the resources currently allocated to each process, and
      the future requests and releases of each process, to decide
      whether the could be satisfied or must wait to avoid a
      possible future deadlock.
49.What are a safe state and an unsafe state?

A state is safe if the system can allocate resources to
      each process in some order and still avoid a deadlock. A system
      is in safe state only if there exists a safe sequence. A sequence
      of processes <P1,P2,....Pn> is a safe sequence for the current
      allocation state if, for each Pi, the resource that Pi can still
      request can be satisfied by the current available resource plus
      the resource held by all the Pj, with j<i. if no such sequence
      exists, then the system state is said to be unsafe.
50.What is banker's algorithm?
            Banker's algorithm is a deadlock avoidance algorithm that
      is applicable to a resourceallocation system with multiple
      instances of each resource type.
      The two algorithms used for its implementation are:
            a. Safety algorithm: The algorithm for finding out whether
      or not a system is in a safe state.
            b. Resourcerequest algorithm: if the resulting resource
      allocation is safe, the transaction is completed and process Pi
      is allocated its resources. If the new state is unsafe Pi must
      wait and the old resourceallocation state is restored.
51.Define logical address and physical address.
             An address generated by the CPU is referred as logical
      address. An address seen by the memory unit that is the one
      loaded into the memory address register of the memory is commonly
      referred to as physical address.
52.What is logical address space and physical address space?
             The set of all logical addresses generated by a program is
      called a logical address space; the set of all physical addresses
      corresponding to these logical addresses is a physical address
      space.
53.What is the main function of the memorymanagement unit?
             The runtime mapping from virtual to physical addresses is
      done by a hardware device called a memory management unit (MMU).
54.Define dynamic loading.
             To obtain better memoryspace utilization dynamic loading
      is used. With dynamic loading, a routine is not loaded until it
      is called. All routines are kept on disk in a relocatable load
      format. The main program is loaded into memory and executed. If
      the routine needs another routine, the calling routine checks
      whether the routine has been loaded. If not, the relocatable
      linking loader is called to load the desired program into memory.
55.Define dynamic linking.
             Dynamic linking is similar to dynamic loading, rather that
      loading being postponed until execution time, linking is
      postponed. This feature is usually used with system libraries,
      such as language subroutine libraries. A stub is included in the
      image for each libraryroutine reference. The stub is a small

piece of code that indicates how to locate the appropriate
      memoryresident library routine, or how to load the library if
      the routine is not already present.
56.What are overlays?
             To enable a process to be larger than the amount of memory
      allocated to it, overlays are used. The idea of overlays is to
      keep in memory only those instructions and data that are needed
      at a given time. When other instructions are needed, they are
      loaded into space occupied previously by instructions that are no
      longer needed.
57.Define swapping.
             A process needs to be in memory to be executed. However a
      process can be swapped temporarily out of memory to a backing
      store and then brought back into memory for continued execution.
      This process is called swapping.
58.What are the common strategies to select a free hole from a set of
   available holes?
             The most common strategies are
                   a. First fit
                   b. Best fit
                  c. Worst fit
59.What do you mean by best fit?
            Best fit allocates the smallest hole that is big enough.
      The entire list has to be searched, unless it is sorted by size.
      This strategy produces the smallest leftover hole.
60.What do you mean by first fit?
            First fit allocates the first hole that is big enough.
      Searching can either start at the beginning of the set of holes
      or where the previous firstfit search ended. Searching can be
      stopped as soon as a free hole that is big enough is found.
61.What is virtual memory?
            Virtual memory is a technique that allows the execution of
      processes that may not be completely in memory. It is the
      separation of user logical memory from physical memory. This
      separation provides an extremely large virtual memory, when only
      a smaller physical memory is available.
62.What is Demand paging?
            Virtual memory is commonly implemented by demand paging. In
      demand paging, the pager brings only those necessary pages into
      memory instead of swapping in a whole process. Thus it avoids
      reading into memory pages that will not be used anyway,
      decreasing the swap time and the amount of physical memory
      needed.
63.Define lazy swapper.
            Rather than swapping the entire process into main memory, a
      lazy swapper is used. A lazy swapper never swaps a page into

memory unless that page will be needed.
64.What is a pure demand paging?
            When starting execution of a process with no pages in
      memory, the operating system sets the instruction pointer to the
      first instruction of the process, which is on a nonmemory
      resident page, the process immediately faults for the page. After
      this page is brought into memory, the process continues to
      execute, faulting as necessary until every page that it needs is
      in memory. At that point, it can execute with no more faults.
      This schema is pure demand paging.
65.Define effective access time.
            Let p be the probability of a page fault (0£p£1). The value
      of p is expected to be close to 0; that is, there will be only a
      few page faults. The effective access time is
            Effective access time = (1p) * ma + p * page fault time.
            ma : memoryaccess time
66.Define secondary memory.
             This memory holds those pages that are not present in main
      memory. The secondary memory is usually a high speed disk. It is
      known as the swap device, and the section of the disk used for
      this purpose is known as swap space.
67.What is the basic approach of page replacement?
             If no frame is free is available, find one that is not
      currently being used and free it. A frame can be freed by writing
      its contents to swap space, and changing the page table to
      indicate that the page is no longer in memory.
             Now the freed frame can be used to hold the page for which
      the process faulted.
68.What are the various page replacement       algorithms used  for   page
replacement?
      • FIFO page replacement
      • Optimal page replacement
      • LRU page replacement
      • LRU approximation page replacement
      • Counting based page replacement
      • Page buffering algorithm.
69.What are the major problems to implement demand paging?
             The two major problems to implement demand        paging   is
      developing
             a. Frame allocation algorithm
             b. Page replacement algorithm
70.What is a reference string?
             An algorithm is evaluated by running it on a particular
      string of memory references and computing the number of page
      faults. The string of memory reference is called a reference
      string.

71.What is a file?
             A file is a named collection of related information that is
      recorded on secondary storage. A file contains either programs or
      data. A file has certain "structure" based on its type.
             • File attributes: Name, identifier, type, size, location,
      protection, time, date • File operations: creation, reading,
      writing, repositioning, deleting, truncating, appending, renaming
             • File types: executable, object, library, source code etc.
72.List the various file attributes.
             A file has certain other attributes, which vary from one
      operating system to another, but typically consist of these:
      Name, identifier, type, location, size, protection, time, date
      and user identification
73.What are the various file operations?
             The six basic file operations are
                   • Creating a file
                   • Writing a file
                   • Reading a file
                   • Repositioning within a file
                   • Deleting a file
                   • Truncating a file
74.What are the information associated with an open file?
            Several pieces of information are associated with an open
      file which may be:
            •  File pointer
            •  File open count
            •  Disk location of the file
            •  Access rights
75.What are the different accessing methods of a file?
            The different types of accessing a file are:
      • Sequential access: Information in the file is accessed
        sequentially
      • Direct access: Information in the file can be accessed without
        any particular order.
      • Other access methods: Creating index for the file, indexed
        sequential access method (ISAM) etc.
76.What is Directory?
            The device directory or simply known as directory records
      informationsuch as name, location, size, and type for all files
      on that particular partition. The directory can be viewed as a
      symbol table that translates file names into their directory
      entries.
77.What are the operations that can be performed on a directory?
            The operations that can be performed on a directory are
      • Search for a file  • Create a file  • Delete  • Rename  • List directory • Traverse the file system
78.What are the most common schemes for defining the logical structure

of a directory?
            The most common schemes for defining the logical structure
      of a directory
      • SingleLevel Directory
      • Twolevel Directory
      • TreeStructured Directories
      • AcyclicGraph Directories
      • General Graph Directory
79.Define UFD and MFD.
            In the twolevel directory structure, each user has her own
      user file directory (UFD). Each UFD has a similar structure, but
      lists only the files of a single user. When a job starts the
      system's master file directory (MFD) is searched. The MFD is
       indexed by the user name or account number, and each entry points
       to the UFD for that user.
80.What is a path name?
             A pathname is the path from the root through all
       subdirectories to a specified file. In a twolevel directory
       structure a user name and a file name define a path name.
81.What are the various layers of a file system?
             The file system is composed of many different levels. Each
       level in the design uses the feature of the lower levels to
       create new features for use by higher levels.
       • Application programs
       • Logical file system
       • Fileorganization module
       • Basic file system
       • I/O control
       • Devices
82.What are the structures used in filesystem implementation?
             Several ondisk and inmemory structures are        used  to
       implement a file system
             a. Ondisk structure include
                   ∙ Boot control block
                   ∙ Partition block
                   ∙ Directory structure used to organize the files
                   ∙ File control block (FCB)
             b. Inmemory structure include
                   ∙ Inmemory partition table
                   ∙ Inmemory directory structure
                   ∙ Systemwide open file table
                   ∙ Perprocess open table
83.What are the functions of virtual file system (VFS)?
             It has two functions
       a. It separates filesystemgeneric operations from their
          implementation defining a clean VFS interface. It allows

transparent access to different types of file systems mounted locally.
       b. VFS is based on a file representation structure, called a
          vnode. It contains a numerical value for a networkwide unique
       file .The kernel maintains one vnode structure for each active
       file or directory.
84.Define seek time and latency time.
             The time taken by the head to move to the appropriate
       cylinder or track is called seek time. Once the head is at right
       track, it must wait until the desired block rotates under the
       readwrite head. This delay is latency time.
85.What are the allocation methods of a disk space?
            Three major methods of allocating disk      space which  are
      widely in use are
      a. Contiguous allocation
      b. Linked allocation
      c. Indexed allocation
86.What are the advantages of Contiguous allocation?
      The advantages are
            a. Supports direct access
            b. Supports sequential access
            c. Number of disk seeks is minimal.
87.What are the drawbacks of contiguous allocation of disk space?
            The disadvantages are
      a. Suffers from external fragmentation
      b. Suffers from internal fragmentation
      c. Difficulty in finding space for a new file
      d. File cannot be extended
      e. Size of the file is to be declared in advance
88.What are the advantages of Linked allocation?
      The advantages are
            a. No external fragmentation
            b. Size of the file does not need to be declared
89.What are the disadvantages of linked allocation?
      The disadvantages are
      a. Used only for sequential access of files.
      b. Direct access is not supported
      c. Memory space required for the pointers.
      d. Reliability is compromised if the pointers are lost or damaged
90.What are the advantages of Indexed allocation?
      The advantages are
            a. No externalfragmentation problem
            b. Solves the sizedeclaration problems.
            c. Supports direct access
91.How can the index blocks be implemented in the indexed allocation
scheme?
            The index block can be implemented as follows

a. Linked scheme
                  b. Multilevel scheme
                  c. Combined scheme
92.Define rotational latency and disk bandwidth.
            Rotational latency is the additional time waiting for the
      disk to rotate the desired sector to the disk head. The disk
      bandwidth is the total number of bytes transferred, divided by
      the time between the first request for service and the completion
      of the last transfer.
93.How freespace is managed using bit vector implementation?
            The freespace 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.
94.Define buffering.
            A buffer is a memory area that stores data while they are
      transferred between two devices or between a device and an
      application. Buffering is done for three reasons
            a. To cope with a speed mismatch between the producer and
      consumer of a data stream
            b.  To adapt between devices that have different data
      transfer sizes
            c. To support copy semantics for application I/O
95.Define caching.
            A cache is a region of fast memory that holds copies of
      data. Access to the cached copy is more efficient than access to
      the original. Caching and buffering are distinct functions, but
      sometimes a region of memory can be used for both purposes.
96.Define spooling.
            A spool is a buffer that holds output for a device, such as
      printer, that cannot accept interleaved data streams. When an
      application finishes printing, the spooling system queues the
      corresponding spool file for output to the printer. The spooling
      system copies the queued spool files to the printer one at a
      time.
97.What are the various diskscheduling algorithms?
            The various diskscheduling algorithms are
      a. First Come First Served Scheduling
      b. Shortest Seek Time First Scheduling
      c. SCAN Scheduling
      d. CSCAN Scheduling
      f. LOOK scheduling
98.What is lowlevel formatting?
            Before a disk can store data, it must be divided into
      sectors that the disk controller can read and write. This process
      is called lowlevel formatting or physical formatting. Lowlevel
      formatting fills the disk with a special data structure for each

sector. The data structure for a sector consists of a header,
      a data area, and a trailer.
99.What is the use of boot block?
            For a computer to start running when powered up or rebooted
      it needs to have an initial program to run. This bootstrap
      program tends to be simple. It finds the operating system on the
      disk loads that kernel into memory and jumps to an initial
      address to begin the operating system execution. The full
      bootstrap program is stored in a partition called the boot
      blocks, at fixed location on the disk. A disk that has boot
      partition is called boot disk or system disk.
100.What is sector sparing?
            Lowlevel formatting also sets aside spare sectors not
      visible to the operating system. The controller can be told to
      replace each bad sector logically with one of the spare sectors.
      This scheme is known as sector sparing or forwarding.

PARTB,C
1. Explain the various types of computer systems.
   Mainframe systems
   Desktop systems
   Multiprocessor systems
   Distributed systems
   Clustered systems
   Realtime systems
   Handheld systems
2. Explain how protection is provided for the hardware resources by the operating
   system.
           Dual mode operation
           I/O protection with diagram
           Memory protection with diagram
           CPU protection
3. What are the system components of an operating system and explain them?
   Process management
   Mainmemory management
   File management
   I/O management
   Secondary storage management
   Networking
   Protection system
   Commandinterpreter system
4. Write about the various system calls.
           Process control
           File management
           Device management
           Information maintenance

Communication
5. What are the various process scheduling concepts
           Scheduling queues with diagram
              Queueing diagram
              Schedulers
              Context switch with diagram
   6. Explain about interprocess communication.
              Messagepassing system
              Naming
              Direct communication
              Indirect communication
              Synchronization
              Buffering
   7. Give an overview about threads.
              Thread definition
              Motivation
              Diagram
              Benefits
              User and kernel threads
   8. Explain in detail about the threading issues.
              The fork and exec system calls
              Cancellation
              Signal handling
              Threads pools
              Threadspecific data
   9. Write about the various CPU scheduling algorithms.
              Firstcome, firstserved scheduling
              Shortestjobfirst scheduling
              Priority Scheduling
              Roundrobin scheduling
              Multilevel queue scheduling
              Multilevel feedback queue scheduling
10.Write notes about multipleprocessor scheduling and realtime scheduling.
              Homogeneous systems
              Load sharing
              Selfscheduling
              Resource reservation
              Priority inversion
               Priority inheritance protocol
               Dispatch latency with diagram
11.What is critical section problem and explain two process solutions and
    multiple process solutions?
               Critical section problem definition
               Two process solutions
               Algorithm 1, 2 & 3
               Multipleprocess solution with algorithm

12.Explain what semaphores are, their usage, implementation given to avoid
   busy waiting and binary semaphores.
               Semaphore definition
               Usage for mutual exclusion and process synchronization
               Implementation to avoid spinlock using block and wakeup
               Binary semaphores
13.Explain the classic problems of synchronization.
               The boundedbuffer problem with structure
               The readerswriters problem with structure
               The diningphilosophers problem with structure
14.Write about critical regions and monitors.
               Critical region definition
               Implementation of the conditionalregion construct
               Monitor definition
               Syntax of monitor
               Schematic view of monitors
               Monitor with condition variables
               Monitor solution to diningphilosopher problem
15.Give a detailed description about deadlocks and its characterization
               Deadlock definition
               Deadlock conditions
               Mutual exclusion
               Hold and wait
               No preemption
               Circular wait
               Resource allocation graph
16.Explain about the methods used to prevent deadlocks
               Ensure that at least one of the following does not hold
               Mutual exclusion
               Hold and wait
               No preemption
               Circular wait
17.Write in detail about deadlock avoidance.
               Safe state and safe sequence
               Diagram for safe, unsafe & deadlock states
               Resourceallocation graph algorithm
18.Explain the Banker's algorithm for deadlock avoidance.
               Deadlock avoidance definition
               Data structures used
               Safety algorithm
               Resource request algorithm
19.Give an account about deadlock detection.
               Single instance of each resource type
               Waitfor graph
               Several instances of a resource type
               Detectionalgorithm usage

20.What are the methods involved in recovery from deadlocks?
               Process termination
               Resource preemption
21.Explain about contiguous memory allocation.
               Contiguous allocation
               Memory protection with diagram
               Memory allocation
               First fit
               Best fit
               Worst fit
               Fragmentation
22.Give the basic concepts about paging.
               Paging definition
               Basic methodpage, frame, page table, page number & page offset
               Paging hardware diagram
               TLB with diagram
               Protectionprotection bits & validinvalid bits
23.Write about the techniques for structuring the page table.
               Hierarchical pagingtwolevel & multilevel with diagram
               Hashed page table with diagram
               Inverted page table with diagram
24.Explain the basic concepts of segmentation.
               User view of program
               Segmentation definition
               Hardware used with diagramsegment table, base, limit & offset
               Protection and sharing with diagram
               Fragmentation
25.What is demand paging and what is its use?
               Demand paging definition
               Virtual memory implementation
               Lazy swapper, page fault, pure demand paging, validinvalid bit
               Diagrams
26.Explain the various page replacement strategies.
               Page replacementbasic scheme with diagram
               FIFO page replacement
               Optimal page replacement
               LRU page replacement
               LRU approximation page replacement
               Countingbased page replacement
               Page buffering algorithm
27.What is thrashing and explain the methods to avoid thrashing?
               Thrashing definition
               Cause of thrashing
               Working set model
               Pagefault frequency
28.What are files and explain the access methods for files?

File definition
               Attributes, operations and types
               Sequential access with diagram
               Direct access
               Other access methodsindex with diagram
29.Explain the schemes for defining the logical structure of a directory.
               Single level directory with diagram
               Two level directory with diagram
               Tree structured directory with diagram
               Acyclicgraph directory with diagram
               General graph directory with diagram
30.Write notes about the protection strategies provided for files.
               Types of access
               Access control list (ACL)
               Three classificationsowner, group & universe
               Other protection approachespasswords
31.Explain the allocation methods for disk space.
               Contiguous allocation advantage, disadvantage & diagram
               Linked allocation advantage, disadvantage & diagram
               Indexed allocation advantage, disadvantage & diagram
               Performance
32.What are the various methods for free space management?
               Bit vector with example
               Linked list with diagram
               Grouping
               Counting
33.Write about the kernel I/O subsystem.
               I/O scheduling
               Buffering
               Caching
               Spooling & device reservation
               Error handling
               Kernel data structures
34.Explain the various disk scheduling techniques
              FCFS scheduling
              SSTF scheduling
              SCAN scheduling
              CSCAN scheduling
              LOOK scheduling
35.Write notes about disk management and swapspace management.
              Disk formattinglow level formatting
              Boot blockbootstrap loader, boot block, boot disk & system disk
              Bad blockssector sparing, sector slipping
              Swapspace use
              Swapspace location
              Swapspace management

Operating System

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