CS 450 Sistemas Operacionais

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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:

SOS, SAGE, SABRE, ATLAS, OS/360, VMS, CTSS, MULTICS, T.H.E., UNIX, CP/M

1. Designed by IBM users ___SOS______

2. Introduced the interrupt concept ___ATLAS____

3. The principal influence for the design of Unix ___MULTICS__

4. The first popular OS for microcomputers ____CP/M____

5. The first timesharing system _____CTSS___

CS 450 – Spring 2009 – Exam 1 Answer Key 4.

5. (15 points: 5 each)

These questions concern the design of a user interface.

a) Identify two tasks normally performed by a terminal handler.

Some examples, as found in the text, include echoing, line buffering, handling break

characters, etc. A brief phrase is sufficient.

b) A common way to confirm a “dangerous” action, such as deleting all files in a

directory, is to ask a question such as “ARE YOU SURE (Y OR N)?” Explain a

problem with this type of confirmation.

The biggest danger with this method is that users will grow overly used to it and type Y

without thinking. If the action is truly drastic, it would be better to use a confirmation

method that forces the user to stop and think for a moment.

c) In spite of the popularity and attractiveness of Graphic User Interfaces (GUIs),

Command Line Interfaces (CLIs) are often used. Give one reason for this.

a. When communicating with a remote server, the CLI greatly reduces

communication costs

b. Scripting is easier

c. More complex parameters and options can be specified simply

6. (10 points: 5 each)

One important criteria for process scheduling is throughput. The goal of throughput is to

get the most work done in a given period of time. Explain briefly two other criteria that might be

appropriate for some schedulers.

1. Turnaround – minimize the time to completion of each job

2. Response time – maintain short and consistent response for interactive users

3. Fairness – Provide the best service to the processes that require it (not

necessarily equal service to all).

ETC.

CS 450 – Spring 2009 – Exam 1 Answer Key 5.

7. (15 points)

Draw a process state diagram with at least five states. Label each state with an appropriate

name. Show the transitions that would normally occur in a nonpreemptive timesharing system.

This diagram shows seven states. Any five are sufficient.