Computer based real time system

DEFINITION:

A real-time system is one that must process information and produce a

response within a specified time, else risk severe consequences, including failure.

That is, in a system with a real-time constraint it is no good to have the correct action

or the correct answer after a certain deadline

• Hard real-time systems

• An overrun in response time leads to potential loss of lifeand/or big financial

damage

• Many of these systems are considered to be safetycritical.

• Sometimes they are “only” mission critical, with themission being very expensive.

• In general there is a cost function associated with thesystem

• Soft real-time systems

Deadline overruns are tolerable, but not desired.• There are no catastrophic

consequences of missing oneor more deadlines.

• There is a cost associated to overrunning, but this costmay be abstract.

• Often connected to Quality-of-Service (QoS)

• Firm teal-time systems

• The computation is obsolete if the job is not finished ontime.

• Cost may be interpreted as loss of revenue.

• Typical example are forecast systems.

• Weakly hard real-time

Systems where m out of k deadlines have to be met.

• In most cases feedback control systems, in whichthe control becomes unstable

with too manymissed control cycles.

• Best suited if system has to deal with otherfailures as well (e.g. Electro

MagneticInterference EMI).

• Likely probabilistic guarantees sufficient.