Client–server model
A shared resource may be any of the server computer's software and electronic components, from programs and data to processors and storage devices.
Generally, a service is an abstraction of computer resources and a client does not have to be concerned with how the server performs while fulfilling the request and delivering the response.
The client only has to understand the response based on the relevant application protocol, i.e. the content and the formatting of the data for the requested service.
A computer can only perform a limited number of tasks at any moment, and relies on a scheduling system to prioritize incoming requests from clients to accommodate them.
An application server interprets the returned data by applying the bank's business logic and provides the output to the webserver.
For example, an attacker might exploit an SQL injection vulnerability in a web application in order to maliciously change or gain unauthorized access to data in the server's database.
[8][9][10] In the case of distributed computing projects such as SETI@home and the Great Internet Mersenne Prime Search, while the bulk of the operations occur on the client side, the servers are responsible for coordinating the clients, sending them data to analyze, receiving and storing results, providing reporting functionality to project administrators, etc.
Additionally, if operations can be performed by the client, without sending data over the network, they may take less time, use less bandwidth, and incur a lesser security risk.
Alternatively, an attacker might employ cross-site scripting vulnerabilities to execute malicious code on the client's system without needing to install any permanently resident malware.
[8][9][10] Distributed computing projects such as SETI@home and the Great Internet Mersenne Prime Search, as well as Internet-dependent applications like Google Earth, rely primarily on client-side operations.
They initiate a connection with the server (either in response to a user query, as with Google Earth, or in an automated fashion, as with SETI@home), and request some data.
The client then analyzes the data (a client-side operation), and, when the analysis is complete, displays it to the user (as with Google Earth) and/or transmits the results of calculations back to the server (as with SETI@home).
In the context of the World Wide Web, commonly encountered computer languages which are evaluated or run on the client side include:[5] An early form of client–server architecture is remote job entry, dating at least to OS/360 (announced 1964), where the request was to run a job, and the response was the output.
Another DEL-capable computer, the server-host, received the packets, decoded them, and returned formatted data to the user-host.
Development of DEL was just beginning in 1969, the year that the United States Department of Defense established ARPANET (predecessor of Internet).
An early use of the word client occurs in "Separating Data from Function in a Distributed File System", a 1978 paper by Xerox PARC computer scientists Howard Sturgis, James Mitchell, and Jay Israel.
In contrast, a rich client, such as a personal computer, has many resources and does not rely on a server for essential functions.
As microcomputers decreased in price and increased in power from the 1980s to the late 1990s, many organizations transitioned computation from centralized servers, such as mainframes and minicomputers, to rich clients.
[17] This afforded greater, more individualized dominion over computer resources, but complicated information technology management.
This maturation, more affordable mass storage, and the advent of service-oriented architecture were among the factors that gave rise to the cloud computing trend of the 2010s.
The computing power, memory and storage requirements of a server must be scaled appropriately to the expected workload.
[citation needed] If a node becomes unavailable, its shared resources remain available as long as other peers offer it.
