Posts

Distributed Client Server Architectures

•A single logical database spread physically across computers in multiple locations that are connected & communicated by a data communications link (high-speed networks or telephone lines). •They do not share main memory or disks. •The computers in a distributed system may vary in size and function, ranging from workstations up to mainframe systems. Major Objectives •Location Transparency –User does not have to know the location of the data –Data requests automatically forwarded to appropriate sites •Local Autonomy –Local site can operate with its database when network connections fail –Each site controls its own data, security, logging, recovery The computers in a distributed system are referred to by a number of different names, such as sites or nodes, depending on the context in which they are mentioned. Advantages and Disadvantagesof DDB •Advantages  i) Sharing data ii) Autonomy iii) Availability •Disadvantages i) Software cost and complexity ii) Proces
Post a Comment
Read more

Switched-based

Image
Switched systems do not have a single backbone like cable television. Instead, there are individual wires from machine to machine, with many different wiring patterns in use. Messages move along the wires, with an explicit switching decision made at each step to route the message along one of the out-going wires. The worldwide public telephone system is organized in this way.   Switched Multiprocessors   To form a Switched Multiprocessors system with more than 64 processors, we need different methods to connect the CPUs with the memory. ● A Crossbar Switch & ● An Omega Switching Network ● NonUniform Memory Access A Crossbar Switch Each CPU and each memory (memory divided into modules) has a connection coming out of it, at every intersection is a tiny electronic crosspoint switch that can be opened and closed in hardware, as shown in Fig.6. When a CPU wants to access a particular memory, the crosspoint switch connecting them is closed momentarily, to allow the access
Post a Comment
Read more

Multiprocessors and Multicomputer

Image
Even though all distributed systems consist of multiple CPUs, there are several different ways the hardware can be organized, especially in terms of how they are interconnected and how they communicate. Various classification schemes for multiple CPU computer systems have been proposed over the years, but none of them have really caught on and been widely adopted. Flynn picked two characteristics that he considered essential: The number of instruction streams and The number of data streams. Flynn’s Classification for multiple CPU computer systems ● SISD A computer with a single instruction stream and a single data stream is called SISD. All traditional uniprocessor computers (i.e., those having only one CPU) fall in this category, from personal computers to large mainframes. ● SIMD Computer with a single instruction stream and multiple data stream is called SIMD. For example, adding(Single Instruction) up all the elements(multiple data) of 64 independent vectors. ● MI
Post a Comment
Read more

Why do we need Distributed System?

Advantages of Distributed Systems Performance: very often a collection of processors can provide higher performance (and better price/performance ratio) than a centralized computer. Distribution: many applications involve, by their nature, spatially separated machines (banking, commercial, automotive system). Reliability (fault tolerance): if some of the machines crash, the system can survive. Incremental growth: as requirements on processing power grow, new machines can be added incrementally. Sharing of data/resources: shared data is essential to many applications (banking, computer supported cooperative work, reservation systems); other resources can be also shared (e.g. expensive printers). Communication: facilitates human-to-human communication. Disadvantages of Distributed Systems Difficulties of developing distributed software: how should operating systems, programming languages and applications look like? Networking problems: several problems are created
Post a Comment
Read more

Applications Distributed Systems

Telecommunication networks Telephone networks and cellular networks. Computer networks such as the Internet. Wireless sensor networks. Routing algorithms.   Network applications World Wide Web and peer-to-peer networks Massively multiplayer online games and virtual reality communities. Distributed databases and distributed database management systems. Network files systems. Distributed information processing systems such as banking systems and airline reservation systems. Real-time process control Aircraft control systems. Industrial control systems.   Parallel computation Scientific computing, including cluster computing and grid computing and various volunteer computing projects; see the list of distributed computing projects. Distributed rendering in computer graphics.
Post a Comment
Read more

Goals of Distributed Systems

The key purposes of the distributed systems can be represented by : • Connecting Users and Resources • Transparency • Communication • Performance & scalability • Heterogeneity • Openness • Reliability & fault tolerance • Security
Post a Comment
Read more

Examples Of Distributed System

Network of workstations Work flow information system supporting automatic order processing. World Wide Web Automatic banking (teller machine) systematic. Inventory Management Supply Chain Management Reservation System University Counselling Online Chain Management.
Post a Comment
Read more