Operating Systems Previous Year Questions (page 2)

Explanation

TLB hit ratio 70%, TLB search 30 ns, memory access 90 ns. On a hit, the page is found in the TLB (30 ns); on a miss, the TLB is searched and the page table read from memory (30 + 90 ns); then 90 ns to access the data. Total = (0.7 × 30) + (0.3 × (90 + 30)) + 90 = 21 + 36 + 90 = 147 ns

Explanation

The correct match: A. Device controller – i. Extracts information from the controller register and stores it in data buffer; B. Device driver – iii. Performs data transfer; C. Interrupt handler – iv. Processing of I/O request; D. Kernel I/O subsystem – ii. I/O scheduling.

Explanation

(1) First come – first served – No starvation (2) Round robin – No starvation (3) Priority – starvation if higher priority process called again & again lower priority starves (4) Shortest process next = starvation possible (5) Shortest remaining time first = starvation possible

Explanation

A distributed operating system is usually defined as running on more loosely coupled hardware. There is no shared memory, but provides a single memory by tightly coupled software.

Explanation

Software engineering is an engineering discipline that is concerned with all aspects of software production.

Explanation

Mccalls's software quality factors. (1) ability to undergo change (2) Adaptability to new environments (3) Operational characteristics but production costs & scheduling is not the aspect of quality factor.

Explanation

Fair-share scheduling is a scheduling algorithm in which CPU usage is equally distributed among system users or groups, rather than equally among processes. The priority considers processor utilization by the individual process, by the user or group, and the weight assigned to the user or group, so (A), (B) and (C).

Explanation

User level threads – advantages: thread switching does not require kernel mode privileges; they can run on any OS; they are fast to create and manage. Disadvantages: in a typical OS most system calls are blocking, so if one user level thread executes a system call, all threads of that process are blocked; and a multithreaded application cannot take advantage of multiprocessing.

Explanation

'init' (PID 1) is not the first process in the system; it is the second, since the scheduler/swapper process (PID 0) is created first. So statement (c) is not correct.

Explanation

Virtual memory maps the virtual addresses used by a program into physical addresses. It provides more addressable memory, allows programs larger than physical memory to run, and allows easy swapping; it does not require more I/O. So 'More I/O is required' is incorrect.

Explanation

The dispatcher is the module that gives control of the CPU to the process selected by the short-term scheduler.

Explanation

In statement set (A), the many-to-one model maps many user threads to one kernel thread, the one-to-one model maps one user thread to one kernel thread, and the many-to-many model maps many user threads to a smaller or equal number of kernel threads; all are true. Set (B) reverses the roles of user and kernel threads, so it is false.

Explanation

For this reference string with 3 frames, the optimal algorithm gives 9 page faults, fewer than FIFO, LIFO or LRU. So the optimal algorithm has the minimum number of page faults.

Explanation

UNIX provides read, write and execute permissions on files, and three sets of permissions: for the owner, for the group and for others. So both (A) and (B) are true.