分布式35998.ppt

分布式系统课程 Introduction Chapter 1 1.1 Definition of a Distributed System A distributed system is a collection of independent computers that appears to its users as a single coherent system. 通过网络互联，可协作执行某个任务的独立计算机集合。 有两个含义： 1、从硬件角度来讲，各个计算机都是自治的，通过网络互联； 2、从软件角度来讲，用户将整个系统看作是一台计算机。 Internet平台的特征 Transparency in a Distributed System Scalability Problems Scaling Techniques (1) Scaling Techniques (2) 1.3 Hardware Concepts Multiprocessors (1) A bus-based multiprocessor. Multiprocessors (2) Homogeneous Multicomputer Systems 1.4 Software Concepts An overview between DOS (Distributed Operating Systems) NOS (Network Operating Systems) Middleware Distributed Operating Systems (1. Uniprocessor Operating Systems)DOS在功能上同UOS 2. Multiprocessor Operating Systems ? 3. Multicomputer Operating Systems Uniprocessor Operating Systems 单机操作系统可以有多种结构实现，目的是管理整个计算机系统的资源，并为用户提供使用上的方便。 操作系统的结构：模块结构；层次结构；微内核结构；面向对象等。 Uniprocessor Operating SystemsSeparating applications from operating system code through a microkernel. Multiprocessor Operating Systems (1) Multiprocessor Operating Systems aim to support high performance through multiple CPUs. An important goal is to make the number of CPUs transparent to the application. Achieving such transparency is relatively easy because the communication between different parts of application uses the same primitives as those in multitasking uniprocessor operating systems. Two important primitives are semaphores and monitors(只需保护数据不在同一时刻受到多个访问) Multiprocessor Operating Systems (1) A monitor to protect an integer against concurrent access. Multiprocessor Operating Systems (2)A monitor to protect an integer against concurrent access, but blocking a process. Multicomputer Operating Systems (1) General structure of a multicomputer operating system(through message passing) 松耦合硬件上的紧耦合软件，系统目标是使用户产生一个视觉：整个计算机网络是一个分时系统，而不是一个互不相同的机器的集合。(没有共享存储, 只能消息传递) Multicomputer Operating Systems (2) Alternatives for blocking and buffering in message passing.(four possib