硬实时任务和软实时任务的区别

实时任务通常分为 – 硬和软，但在广泛的范围内，实时任务分为：

1. 硬实时任务
2. 实时任务
3. 软实时任务

1. 固定实时任务：
固定实时任务是这类具有时间限制的实时任务，任务需要在截止日期内产生结果。虽然固定实时任务与硬实时任务不同，因为在硬实时中，一旦超过截止期限而任务没有完成，系统就会失败，但如果是固定实时任务，即使超过了截止期限，系统也会执行不会失败。

例子：

1. Video conferencing
2. Satellite based tracking 

2. 软实时任务：
软实时任务是此类实时任务，它们也与时间限制相关联，但这里的时间限制不表示为绝对值。在软实时任务中，即使在截止日期之后结果也不会被认为是错误的，也不会发生系统故障。

例子：

1. Web browsing
2. Railway Ticket Reservation 

硬实时任务和软实时任务的区别：

FIRM REAL-TIME TASKS	SOFT REAL-TIME TASKS
It needs to be completed within the deadline.	It also needs to be completed within deadline but not strictly.
The value of associated timing constraint is taken as absolute.	The value of associated timing constraint is taken as average value.
The utility of result becomes zero after the deadline.	The utility of result decreases after the deadline but it gradually becomes zero.
Result obtained after deadline is considered incorrect.	Result obtained after deadline is not incorrect.
It is widely used in multimedia applications.	It is less used in such applications.
It is less used in practical applications.	It is widely used in practical applications.
Example: Satellite based tracking.	Example: Railway ticket reservation.