A distributed system is defined as a collection of computers connected by a network, and with the appropriate distributed software so that the system is seen by users as a single entity capable of providing computing facilities. Distributed systems are implemented on various hardware platforms, from a few workstations connected by a local area network, to the Internet, with a collection of extensive interconnected networks, which link millions of computers.
Key characteristics of Distributed Systems
- Each item of computation has its own memory and its own Operating System.
- Control of local and remote resources.
- Open Systems (Facilities for change and growth).
- Non-standard platform (Unix, NT, Intel, RISC, Etc.).
- Media (Networks, Protocols, Devices, Etc.).
- Processing capacity in parallel.
- Dispersion and bias.
Main characteristics that define them:
The resources in a distributed system are physically encapsulated in one of the computers and can only be accessed by other computers through the network. For the sharing of resources to be effective, it must be managed by a program that offers a communication interface allowing the resource to be accessed, manipulated and updated in a reliable and consistent manner, this program is the resource manager.
A system can be open or closed with respect to hardware extensions or with respect to software extensions. The opening of distributed systems is mainly determined by the degree to which new resource sharing services can be added without harming or duplicating existing ones.
When there are several processes in a single machine we say that they are running concurrently. If the computer is equipped with a single central processor, the concurrency takes place interlacing the execution of the different processes.
Distributed systems operate effectively and efficiently at many different scales. The smallest scale consists of two work stations and a file server, when the size and complexity of computer networks grows, it is a prime objective to design distributed system software that will remain efficient and useful with these new network configurations. .
Computer systems sometimes fail. When software or hardware failures occur, the programs may produce incorrect results or may stop before completing the process they were performing. The design of fault tolerant systems is based on two complementary issues: Hardware redundancy and software recovery.
The transparency of a distributed system goes hand in hand with the fact that the whole system works in a similar way in all network points, regardless of the user’s position, this mechanism allows all users to work as if it were a single computer.
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Advantages of distributed systems
- Economy: Microprocessors offer a better price / performance ratio than mainframes.
- Speed: It has more computing power than a mainframe.
- Inherent distribution: Applications in geographically separated machines.
- Reliability: The system survives any failure in a machine.
- Shared Data: Users have access to a common database.
- Shared Devices: Users share expensive peripherals.
- Communication: facilitates person-to-person communication.
- Flexibility: Diffuses the load between the available machines in an efficient way.
Disadvantages of distributed systems
- Software: There is little software available for distributed systems. The algorithm is less controllable.
- Networks: They can become saturated or cause other problems.
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