ITPEC FE Morning April 2021 Question 74
When real-time systems are classified into hard real-time and soft real-time systems, which of the following is in the category of a hard real-time system?
Explanation
Airbag control system — missing its deadline even once can cost lives, so it is hard real-time.
In a hard real-time system a result delivered after the deadline is worthless or dangerous, so the deadline must always be met. An airbag must inflate within a few tens of milliseconds of a collision; late inflation fails to protect the occupant. In a soft real-time system a late response only lowers the quality of service, and the system is still useful.
Answer (a)
Why not others:
- •(b) Bank ATM system — a slow transaction annoys the customer but causes no damage; soft real-time
- •(c) Seat reservation system — a delayed response is an inconvenience; soft real-time
- •(d) Web delivery system — late content degrades the experience but can still be used; soft real-time
Key rule: Ask what happens when the deadline is missed: catastrophe or total failure means hard real-time (airbags, brakes, flight control); degraded service means soft real-time.
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