Applications, advantages of DS

Principal applications

• World Wide Web and Internet services: web hosting, e-mail, search.
• Banking and finance: ATM networks, online banking, stock exchange.
• Telecommunication: mobile networks, VoIP.
• Cloud computing: storage and computing services such as AWS, Google Drive.
• Distributed databases and file systems: NFS, Google File System, the databases behind e-commerce sites.
• Scientific computing / grid: weather forecasting, SETI@home, genome analysis.
• Multimedia and entertainment: video on demand, online games.
• Air/railway reservation, e-governance and sensor/IoT networks.

Advantages

• Economics: many cheap computers give a better price/performance ratio than one mainframe.
• Performance and speed: work is shared among processors (parallel processing, load balancing).
• Inherent distribution: applications such as banking, e-mail and the web are naturally spread over many places.
• Reliability and availability: if one machine fails the others continue, particularly with replication.
• Resource sharing: hardware, software and data are shared by remote users.
• Incremental growth (scalability): capacity is added by adding machines.
• Flexibility and openness: parts from different vendors can be combined.

Disadvantages

• Complexity: design, development and debugging are harder than for a single machine.
• Software: little general-purpose distributed software exists; middleware adds overhead.
• Network problems: the network may be slow, saturated or fail, and lost messages hurt the system.
• Security: open networks and shared resources raise the risk of attacks and data leakage.
• Partial failure: parts fail independently, so the state is hard to know and keep consistent.
• No global clock or shared memory: synchronisation and agreement are difficult.
• Higher management cost: many machines need to be administered, upgraded and kept consistent.