CS 450 Sistemas Operacionais

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EXAM 1

CS 450 – Spring 2009

ANSWER KEY

Lane Department of Computer Science and Electrical Engineering

West Virginia University

Feb. 25, 2009

This is a closed book test. No notes or other resources are allowed. Read each question

carefully and pace yourself. Put all answers on the exam paper, in the space provided.

1. (20 points: 2 each)

TRUE OR FALSE

a) UNIX was originally designed as a single-user OS TRUE

b) OS/360 was delivered on time and with few bugs. FALSE

OS/360 was years late and hundreds of bugs were found.

c) Timesharing was not feasible before the development of file systems. TRUE

d) A user interface interacts with the OS though the program interface. TRUE

e) Command languages do not provide conditional and loop structures,

since they would have no use. FALSE

These structures are important in scripts and CLI programs

f) A system call is often implemented as a type of interrupt. TRUE

g) Some OSs provide ID numbers for processes, but every system

requires processes to have names. FALSE

Process IDs are always used. Names are optional.

h) A process must always be in the ready state before changing to the

running state. TRUE

i) A drawback of shortest-job-first scheduling is that it may make long

jobs wait forever. TRUE

j) When scheduling with feedback queues, highly interactive processes

should be assigned high priorities and short time quanta. TRUE

CS 450 – Spring 2009 – Exam 1 Answer Key 2.

2. (20 points: 4 each)

Explain briefly each of the following terms.

a) Logical resource

A resource that is information rather than a physical object. Examples are files, data

structures, processes

b) Keyword arguments

Command Language arguments that are identified by a string name, for example,

SOURCE=FILE1. Contrasts with positional arguments.

c) Astonishment Factor

A characteristic of some user interface elements that causes the user to be “astonished”

when the interface does something unexpected. One cause of this might be automatic

command completion.

d) Aging

A strategy for avoiding “starvation” (indefinite delay of low-priority processes) in a

priority-based scheduler such as SJF. Periodically, the priority of all processes is raised.

Eventually, long-waiting processes will have their priority raised enough that they will be

scheduled.

e) Interrupt Vector

A small block of memory, usually at the lowest addresses, dedicated to handling a

particular interrupt. The interrupt vector specifies where the handler is located and may

provide storage for saving critical state information.

CS 450 – Spring 2009 – Exam 1 Answer Key 3.

3. (10 points)

An operating system is a manger of resources. Identify the two principal objectives of

resource management, and give a brief example for each objective.

1) Convenient use. An example is a file system, which makes it much more convenient to

manage information on a storage device.

2) Controlled sharing. An example is a device allocation routine, which ensures that only

one process at a time is permitted to use a particular device.

4. (10 points)

Match an OS from the list given to each of the descriptive phrases below. You may use the

same name more than once. Here is the list: