Operating System Interview Questions and Answers
Question - 71 : - Why is interrupt vector used in operating systems?
Answer - 71 : - 1. The operating system these days are interrupt driven and this requires the interrupt vector.
2. This interrupt vector contains the addresses of the interrupt service routines for various devices.
3. Here the interrupts can be indirectly called through the table with no intermediate routine needed.
4. This leads to interrupt handling at a faster rate.
5. Operating systems like MS DOS and UNIX are using the interrupt vector.
Question - 72 : - What is the need of device status table?
Answer - 72 : - 1. This table gives the device type, its address and status.
2. It is required to keep a track of many input output requests at the same time.
3. The state of the device can be functioning, idle or busy.
4. If a device is busy, type of request and other parameters are stored in the table entry.
5. If more than one processor issues request for the same device then a wait queue is maintained.
Question - 73 : - How can the speed of interrupt driven input output systems be improved?
Answer - 73 : - 1. Direct memory access is used to enhance the speed of the input output systems.
2. Here, buffers, counters and pointers are set for the devices.
3. The device controller transfers the block of data directly from own buffer storage to memory.
4. The data is not given to the CPU for further transfer between CPU and input output devices or CPU and memory.
5. Only one interrupt is generated per block than one interrupt per byte which enhances the speed.
Question - 74 : - Explain the execution cycle for a von Neumann architecture.
Answer - 74 : - 1. Initially the system will fetch the instruction and stores it in instruction register.
2. Instruction is then decoded and may cause operands to be fetched from memory.
3. After execution the result is stored in the memory.
4. Here the memory unit sees only the memory addresses irrespective of how they are generated.
5. Memory unit is also unaware of what addresses are for
Question - 75 : - Explain the positioning time for a disk.
Answer - 75 : - 1. It is also called as the random access time used by a disk to perform operations.
2. It consists of time to move the disk arm to the desired cylinder called the seek time.
3. The time required for the desired sector to rotate to the disk head is called rotational latency.
4. Typical disks can transfer megabytes of data per second.
5. Seek time and rotational latency is always in milliseconds.
Question - 76 : - What is EIDE?
Answer - 76 : - 1. EIDE is a bus called enhanced integrated drive electronics.
2. The input output devices are attached to the computer by a set of wires called the bus.
3. The data transfer on a bus are carried out by electronic processes called controllers.
4. The host controller sends messages to device controller and device controller performs the operations.
5. These device controllers consist of built in cache so that data transfer occurs at faster speed.
Question - 77 : - Differentiate between the user mode and monitor mode.
Answer - 77 : - 1. User mode and monitor mode are distinguished by a bit called the mode bit.
2. User mode uses bit 1 and monitor mode uses bit 0.
3. At the boot time hardware starts with the monitor mode.
4. Also, at the time of interrupt user mode is shifted to the transfer mode.
5. System always switches to the user mode before passing control to the user program.
6. Whenever system gains control of the computer it works in monitor mode otherwise in user mode.
Question - 78 : - What is time slice?
Answer - 78 : - 1. The timer in CPU is set to interrupt every N milliseconds where this N is called the time slice.
2. It is the time each user gets to execute before control is given to next user.
3. At the end of each time slice the value of N is incremented and the record is maintained.
4. It also maintains the record of the total time user program has executed thus far.
5. This method helps in time sharing among the various users.
Question - 79 : - What are the activities related to the Time Shared User Program Management?
Answer - 79 : - 1. An Operating System is responsible for the creation and deletion of both user and system processes.
2. It also provides mechanism for the process synchronization.
3. Suspending and resuming of windows is done by the operating system itself.
4. Program needs resources like CPU time, memory, files, input output devices to complete the task which is provided by the operating system.
5. Mechanisms are also provided for deadlock handling.
Question - 80 : - When an input file is opened, what are the possible errors that may occur?
Answer - 80 : - 1. 1st condition may be that the file is protected against access, here it terminates abruptly.
2. 2nd condition may be that file exists, then we need to create the output file.
3. If file with the same name exists then it may be deleted or program may be aborted.
4. In another case the system may ask the user to replace the existing file or abort the program.