What is a distributed system
According wekipedia, distributed computing study coordinated use of the computer that is physically separated or distributed. Distributed systems requires different software with a centralized system.
As for other opinions:

A reply system components are located on computer networks. Tsb components communicate with each other & to coordinate only with sending messages (message passing) and has a coordination process through the exchange of synchronous or asynchronous message

Collection of independent computers that appear as a single user computer system

Collection of autonomic computers connected by a network with software designed to produce an integrated computing facility

Computer Network vs. Distributed Systems
? Computer networks

1. the autonomous commuter explicitly visible (explicitly teralamati)

? Distributed Systems

1. the existence of several autonomous computers is transparent
2. Normally, every distributed system relies on services provided by computer network
3. Some services on computer networks (such as, name service) is also a distributed system
4. Distributed Systems more problems faced by

Reasons for distributed systems
? Distribution function: the computer has the ability functions different
- Client / server
- Host / terminal
- Data gathering / data processing
? Load distribution / balance: giving tasks to the processor enough so that the performance of the entire
optimized system.
? The nature of the distributed application prevent domain, e.g.
- Cash register and inventory system for supermarkets,
- Computer support collaborative work

? replication processing power: independent processors working for the same job
- Distributed system consists of a collection of microcomputers have the processing power that can not be achieved by supercomputers
10,000 ? CPU, each running at 50 MIPS, MIPS reached 500,000,
- So one command executed in 0002 nsec
? Physical separation: systems that rely on the fact that computers are physically separated (eg, to achieve reliability).
? Economies: a collection of microprocessors offer price / performance is better than the mainframe

Examples of Distributed Systems

• Internet

• intranet

• mobile computing