A real-time operating system is an operating system intended to serve real-time applications that process data as it comes in, typically without delay. Real-time system can be classified into two:
- Hard Real Time Systems
- Soft Real Time Systems
Hard Real Time System (Immediate Real-Time System)
A hard real-time system also referred to as immediate real-time system is a hardware or software that must operate within the confines of a stringent predefined deadline. Usually the application is considered to have failed if it does not complete its function within the specified timeline. The response predefined time of hard real time systems is in order of milliseconds and therefore, missing of the deadline results in complete or massive system failure, and therefore this system should not miss the deadline.
Examples of hard real time system are:
- Inkjet printer system
- Railway signaling system
- Air traffic control systems
- Nuclear reactor control systems
- Anti-missile system
What You Need To Know About Hard Real Time System
- Size of the data file in soft real time systems is small or medium.
- Examples of hard real time system are inkjet printer system, railway signaling system, air traffic control systems, nuclear reactor control systems, anti-missile system.
- A hard-real time system is very restrictive.
- The response predefined time of hard real time systems is in order of milliseconds and therefore, missing of the deadline results in complete or massive system failure, and therefore this system should not miss the deadline.
- Peak load performance should be predictable and should not violate the predefined deadlines.
- A hard real-time system must remain synchronous with the state of the environment at all time.
- Most of the hard real time systems have small databases and occasionally require short-term integrity of the system.
- In case of an error in a hard real time system, the computation is rolled back or recovery is of limited use.
- Completion of the task or activity by hard real time systems is predefined or deterministic.
- The users of hard real time systems obtain validation when required.
Soft Real Time System
Soft real-time system is an operating system in which a critical real-time task gets priority over other task and retains that priority over other tasks until it completes. The response predefined time of soft real time systems are not very stringent, therefore missing of the deadline only affects the performance and not the entire system.
Examples of soft real time systems are:
- DVD player
- Electronic games,
- Multimedia system
- Web browsing
- Online transaction systems
- Telephone switches
- Virtual reality
- Weather station
- Mobile communication etc.
What You Need To Know About Soft Real Time System
- Size of the data file in soft real time systems is large.
- Examples of soft real time systems are DVD player, electronic games, multimedia system, web browsing, online transaction systems, telephone switches, virtual reality, weather station, mobile communication etc.
- Soft real time system is less restrictive in nature.
- The response predefined time of soft real time systems are not very stringent, therefore missing of the deadline only affects the performance and not the entire system. Soft real time systems misses deadline occasionally.
- In a soft real time system a degraded operation in a rarely occurring peak load can be tolerated.
- Soft real time system will slow down their response time if the load is very high.
- Most of the soft real time systems have larger databases and require long-term integrity of the system.
- In case of an error in a soft real time system, the computation is rolled back to previously established checkpoint to initiate a recovery action.
- Completion of task or activity by soft real time system probabilistic.
- Users of soft real time systems not always obtain the validation.
Difference Between Hard Real Time System And Soft Real Time System In Tabular Form
| BASIS OF COMPARISON | HARD REAL TIME SYSTEM | SOFT REAL TIME SYSTEM |
| Data File Size | Size of the data file in soft real time systems is small or medium. | Size of the data file in soft real time systems is large. |
| Example | Examples of hard real time system are inkjet printer system, railway signaling system, air traffic control systems, nuclear reactor control systems, anti-missile system. | Examples of soft real time systems are DVD player, electronic games, multimedia system, web browsing, online transaction systems, telephone switches, virtual reality, weather station, mobile communication etc. |
| Restrictive Nature | A hard-real time system is very restrictive. | Soft real time system is less restrictive in nature. |
| Response Time | The response predefined time of hard real time systems is in order of milliseconds and therefore, missing of the deadline results in complete or massive system failure, and therefore this system should not miss the deadline. | The response predefined time of soft real time systems are not very stringent, therefore missing of the deadline only affects the performance and not the entire system. Soft real time systems misses deadline occasionally. |
| Peak Load | Peak load performance should be predictable and should not violate the predefined deadlines. | In a soft real time system a degraded operation in a rarely occurring peak load can be tolerated. |
| Conditional Requirement | A hard real-time system must remain synchronous with the state of the environment at all time. | Soft real time system will slow down their response time if the load is very high. |
| Database Size & Integrity | Most of the hard real time systems have small databases and occasionally require short-term integrity of the system. | Most of the soft real time systems have larger databases and require long-term integrity of the system. |
| Error Handling | In case of an error in a hard real time system, the computation is rolled back or recovery is of limited use. | In case of an error in a soft real time system, the computation is rolled back to previously established checkpoint to initiate a recovery action. |
| Completion Of Task/Activity | Completion of the task or activity by hard real time systems is predefined or deterministic. | Completion of task or activity by soft real time system probabilistic. |
| Validation | The users of hard real time systems obtain validation when required. | Users of soft real time systems not always obtain the validation. |