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IT342 Operating Systems for Administrators 17 October, 2006 MIDTERM EXAMINATION (A) 19:30 — 21:
INSTRUCTIONS:
(1) Answer all questions directly on the examination paper. (2) No notes, books, or other aids are permitted. No electrically operated aid devices are permitted, in- cluding, but not limited to, computers, calculators, cellular phones, pagers, or PDA devices. (3) If the space allotted for your answer is too small, continue your answer on the back of the page, clearly indicating your answer is continued overleaf. (4) The exam has 16 questions on 6 pages, apart from this cover page. Attempt all questions: partial marks are given for incomplete but correct answers. (5) Numbers beside questions in [] brackets denote number of points the question is worth. This exam is out of 110 total points.
Good luck!
Points distribution:
Score Question Out of Score Question Out of Score Question Out of
(1) [2] Traps and interrupts are very similar; name one thing that makes interrupts different from traps in the way they are handled.
(2) [2] Arrange in order from longest latency to shortest (i.e., slowest access time to fastest), making sure to indicate which is fastest: optical disk, register, RAM/main memory, magnetic disk, cache
(3) [4] Having detected deadlock, briefly describe two strategies that can be used to correct the prob- lem.
(4) [5] Briefly explain what makes a master/slave multiprocessor different from a symmetric multipro- cessor.
(5) [3] Handling a page fault requires that the missing page to be located on disk and loaded into memory. The wait for this operation is overwhelmingly dominated by the time the disk takes to respond. Briefly describe a situation in which the waiting time (time from when page fault occurs to when the page is available in memory for use) may be twice as long as what is described here.
(6) [2] What does the term cache-hit ratio tell you?
(10) [20] Fill in the blanks:
Data structure where OS keeps administrative & status information about a process:
Number of pages of a process that may appear in a frame of memory at a time:
Part of OS always resident in memory:
UNIX/linux command to send a signal to another process:
Two kinds of semaphores: counting and
What you get when you cannot find a page table entry for a page:
An executable image of a program suitable for loading into memory to be run is a
The time between a user submitting a request and the start of some response is:
Special associative cache memory used to speed up page table look-ups:
Fixed partition allocation schemes suffer from fragmentation.
The only tool that comes standard with Windows for pure plain-text editing:
A synchronization technique that works in all combinations of single/multiple CPUs with sin- gle/multiple memories:
The set of pages of a process present in real memory is the set.
Part of computer that mediates movement of data between CPU and other system compo- nents like memory or peripherals:
To create a new process in any UNIX-style system, first use a system call.
If, on a virtual Windows machine, a user creates and saves 10 new files, how many of these new files are added as new files to what already appears on the hosting sys- tem:
Peripheral devices may be operated using a polling technique, or using
Suppose a system uses 512-byte pages: how many address bits are needed for the offset onto a page (hint: 1024 = 210 ):
A area of code that must not be simultaneously accessed by more than one process is a
A hardware instruction to support mutual exclusion:
(11) [10] A ‘‘page reference string,’’ as we saw in class, is a list of the pages of a process that are refer- enced in sequence as addresses in the program are referenced. For the page reference string: 1 5 1 4 3 2 6 1 show the behaviour of the paging mechanism with 3 frames and indicate where page faults result from use of FIFO page replacement.
FIFO 1 5 1 4 3 2 6 1
frame 0 frame 1 frame 2 PF? y/n
Total page faults (counting initial [i.e., first-time-use of a page] loads):
(12) [3] UNIX/linux provides a signal mechanism as a way for one process to get another’s attention. Suppose processes A wants to send a signal to process B. Can process B itself catch all signals sent to it? Briefly explain why or why not.
(14) [8] Semaphores are a software mechanism designed to provide mutual exclusion. Name and briefly describe the three operations that can be performed on a semaphore.
(15) [5] You note that a computer system is not using its CPU very much, so you arrange to run more processes on it, hoping to keep the CPU busier. As you increase the number of processes on this system you observe that performance becomes drastically worse after a certain point: all processes start taking much longer to run. Up to this point, you discovered that the CPU was, at most, busy 30% of the time running your processes. After this point, that number becomes 0.2%. What do you suspect the problem to be? A manager suggests to you that you should get a faster CPU for the computer: would this help? briefly explain why or why not.
(16) [6] Fill in the blanks in the table below asking about scheduling policies: indicate whether the pol- icy is pre-emptive or not, and for the ‘kinds of jobs’ part, one example is sufficient in each case. Pre- Kind of jobs Kind of jobs emptive? favourable for: unfavourable for:
FIFO
Round-robin
