OS:Concurrent and Distributed Software Design(1)

Chpt1. System design requirements

   We shall study how many applications may be run simultaneously by an operating system and how operating systems support concurrent applications.

 

1.1 Inherently concurrent systems

广义的系统分类:

• Real-time and embedded systems(special-purpose)
• operating systems
• distributed operating systems
• database management and transaction processing systems(run above operating systems)
• distributed, application-level services

1.1.1 Real-time and embedded systems

Characteristic: timing requirements

 

Hard and Soft:

l          hard real-time system: timing requirements are absolute

l          soft real-time system: failing to meet a deadline will not lead to a catastrophe(大灾难).

Static and Dynamic:

l        Static: an analysis of the activities that must be carried out by the system can be done when the system is designed.

l        Dynamic: requests may occur at irregular and unpredictable times and the system must respond dynamically and with guaranteed performance.

 

Real-time dose not always imply “very fast indeed”

 

两个实时系统的例子：

(1)    Process control

(2)    Multimedia support(Qos)

不同场合要求的时实性是不同的，在视频聊天的时候，一些信息的丢失和延迟是可以接受的(soft real-time system)，但是在航空系统、工厂的自动化生产线上的机器人，或者在汽车的自动驾驶系统中，如果信息不能及时处理或者丢失，后果可能会是很严重的(hard real-time system)

 

Requirements：

l        To support separate activities(gathering data, responding alarm signals)

l        To meet the specific requirements of each activity, which may involve meeting time deadlines

l        There may be a need for the separate activities to work together to achieve a common goal

(C) icymoon@NKU