1.4 Defining a concurrent system
The concurrent system may be an operating system, a subsystem within an operating system or an application-level service running above an operating system.
1.5 Systems implementation requirements
(1) Support for separate activities
(2) Support for the management of separate activities
(3) Support for related activities to work together
(4) The ability to meet timing requirements
(5) Support for composite tasks
BTW: nkmxb师兄搜到的一个概念 persistent memory == ROM (-_-#)
1.6 Security, protection and fault tolerance in system design.
安全问题是人的问题。有计算机的地方，就不可避免地存在安全问题。
The topic of security is huge and includes all aspects of controlling access to computers, networks and information stored, processed and transferred in computer systems. We can express a general requirement that it should be possible for policies to be expressed and enforced relating to who (which principals) may have access to computers, networks and information.
几个相关概念：
Memory protection
Access control
Authorization
Encryption
Fault tolerance：最基本的思想是“冗余” 。
/* 摘自《Linux设备驱动程序》的一段话：
区分机制和策略是Unix设计背后隐含的最好的思想之一。大多数编程问题实际上都可以分成两部分：“需要提供什么功能”（机制mechanism）和“如何使用这些功能”（策略）。*/
Chapter 1 describes a number of types of system and draws out requirements for supporting them. Software systems can exploit a wide range of hardware topologies and architectures.
/*这章主要是系统设计的一些需求描述。没有细节上的描述，建立的概念也比较浅。后面将是Part I System design: Technology and principles, Chapter 2 System structure and dynamic execution (系统设计：技术与原理，第2章 系统结构与动态执行)*/
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