Real Time Tasks :
A task whose performance is judged based on deadlines is termed as real time tasks. And the hardware System that handles the real time tasks are called “Real Time Systems”.
There are three types of Real Time Tasks –
- Hard Real Time Tasks
- Soft Real Time Tasks
- Firm Real Time Tasks
These are explained as following below.
1. Hard Real Time Tasks :
In Hard Real Time tasks it is compulsory for a task to be completed within the deadline. Failing to do so results in disastrous effect most of the time and might lead to loss of human lives. If the Hard Real Time tasks misses the deadline that is if C > D where “C” refers to completion time of a task and “D” refers to deadline then the output generated is completely useless. In other words value of outcome is zero and the output is rejected completely.
The System Fails if Hard Real Time tasks misses the deadline.
Required Condition for Hard Real Time tasks : C <= D then Q=1 where C is completion time, D is Deadline and Q is Quality or Significance. And is C > D then Q=0
Examples –
- Air Traffic Control System
- Air Bags Controls in Car
- Anti Missile System
2. Soft Real Time Tasks :
In Soft Real time tasks the deadline is followed but it is not mandatory. This means that even if the deadline is missed the output is not rejected completely. The task that misses the deadline is affected with some penalty or fine in the form of reduced quality of service. As the completion time crosses the deadline the value of the output reduces until it reaches zero that is output is of no use. There are no catastrophic effects or loss of human lives associated in Soft Real Time Tasks on missing the deadline but quality of system drops over the time.
The System keeps on working but the quality is lowered if the deadline is missed.
Required Condition for Soft Real Time tasks : C <= D then Q=1 and if C > D then Q lowers and move till Q=0.
Examples –
- Online Gaming.
- Online Scoreboard. – It is expected to update the scoreboard as soon as the actual game proceed, but even if the results are updated a bit late the scoreboard still shows valid score and are still useful.
3. Firm Real Time Tasks :
Firm Real Time tasks are treated as a combination of Hard Real Time Tasks and Soft Real Time Tasks. In Firm Real Time Tasks if the deadline is missed the value of output is dropped to zero (as done in Hard Real Time Tasks) but still the system is working without any catastrophic effects (as done in Soft Real time Tasks).
The System allows the task to miss the deadline, but not regularly. If tasks misses the deadline commonly or on regular basis the System Failure occur.
Examples:
- Video Processor – Consider a System that processes the video frame by frame and shows continuous video playback. Missing two or three frames in between the complete processing doesn’t cause any disruption in the video playback but missing too many frames leads to interrupted video.