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Leia o texto a seguir, em inglês, e responda às questões de

números 68 a 70.

Computers are used to control a wide range of systems from

simple domestic machines, through games controllers, to entire

manufacturing plants. These computers interact directly with

hardware devices. Their software must react to events generated

by the hardware and, often, issue control signals in response

to these events. These signals result in an action, such as the

initiation of a phone call, the movement of a character on the

screen, the opening of a valve, or the display of the system status.

The software in these systems is embedded in system hardware,

often in read-only memory, and usually responds, in real time, to

events from the system's environment. By real time, I mean that the

software system has a deadline for responding to external events.

If this deadline is missed, then the overall hardware–software

system will not operate correctly.

Embedded software is very important economically because

almost every electrical device now includes software. There are

therefore many more embedded software systems than other

types of software system. If you look around your house you may

have three or four personal computers. But you probably have

20 or 30 embedded systems, such as systems in phones, cookers,

microwaves etc.

Responsiveness in real time is the critical difference

between embedded systems and other software systems, such as

information systems, web-based systems, or personal software

systems, whose main purpose is data processing. For non-realtime

systems, the correctness of a system can be defined by

specifying how system inputs map to corresponding outputs that

should be produced by the system. In response to an input, a

corresponding output should be generated by the system and,

often, some data should be stored. For example, if you choose a

create command in a patient information system, then the correct

system response is to create a new patient record in a database,

and to confirm that this has been done. Within reasonable limits,

it does not matter how long this takes.

However, in a real-time system, the correctness depends both

on the response to an input and the time taken to generate that

response. If the system takes too long to respond, then the required

response may be ineffective. For example, if embedded software

controlling a car braking system is too slow, then an accident

may occur because it is impossible to stop the car in time.

(Extraído de: Software Engineering, I. Sommerville, 9th Edition, 2011, pg. 538.)

Na frase Within reasonable limits, it does not matter how

long this takes., o termo reasonable, no contexto, tem o

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