实时系统被定义为一个系统，其中工作有截止日期，工作必须在截止日期前完成(严格完成)。如果结果延迟，可能会造成巨大的损失。
1. 硬实时系统：
硬实时是指操作不正确，结果不是按时间约束产生的系统。
例如，
1. Air Traffic Control
2. Medical System 2. 软实时系统：
软实时系统是一种系统，如果没有按照指定的时序要求产生结果，则其操作会降级。
例如<
1. Multimedia Transmission and Reception
2. Computer Games 硬实时和软实时系统的区别：
| HARD REAL TIME SYSTEM | SOFT REAL TIME SYSTEM |
|---|---|
| In hard real time system, the size of data file is small or medium. | In soft real time system, the size of data file is large. |
| In this system response time is in millisecond. | In this system response time are higher. |
| Peak load performance should be predictable. | In soft real time system, peak load can be tolerated. |
| In this system safety is critical. | In this system safety is not critical. |
| A hard real time system is very restrictive. | A Soft real time system is less restrictive. |
| In case of an error in a hard real time system, the computation is rolled back. | In case of an soft real time system, computation is rolled back to previously established a checkpoint. |
| Satellite launch, Railway signaling system etc. | DVD player, telephone switches, electronic games etc. |