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Thin client

Thin clients connected to their server via a computer network

A public thin-client computer terminal inside a public library.

An Aleutia E3 thin client, with flash memory

A thin client (sometimes also called a lean, zero orslim client) is a computer or a computer program thatdepends heavily on some other computer (its server) tofulfill its computational roles. This is different from thetraditional fat client, which is a computer designed totake on these roles by itself. The specific roles assumedby the server may vary, from providing data persistence(for example, for diskless nodes) to actual informationprocessing on the client's behalf.

Thin clients occur as components of a broadercomputer infrastructure, where many clients share theircomputations with the same server. As such, thin clientinfrastructures can be viewed as providing somecomputing service via several user interfaces. This isdesirable in contexts where individual fat clients havemuch more functionality or power than theinfrastructure requires.Thin-client computing is also a way of easilymaintaining computational services at a reduced totalcost of ownership.The most common type of modern thin client is alow-end computer terminal which only provides agraphical user interface - or more recently, in somecases, a web browser - to the end user.

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History

A connected SamsungChromebox as seen from above.

Thin clients have their roots in multi-user systems, traditionally mainframesaccessed by some sort of terminal computer. As computer graphics matured, theseterminals transitioned from providing a command-line interface to a full graphicaluser interface, as is common on modern thin clients. The prototypical multiuserenvironment along these lines, Unix, began to support fully graphical X terminals,i.e., devices running display server software, from about 1984. X terminals remainedrelatively popular even after the arrival of other thin clients in the mid-late1990s.[citation needed] Modern Unix derivatives like BSD and GNU/Linux continuethe tradition of the multi-user, remote display/input session. Typically, X software isnot made available on non-X-based thin clients, although no technical reason for thisexclusion would prevent it.[citation needed]

Windows NT became capable of multi-user operations primarily through the effortsof Citrix Systems, which repackaged NT 3.5.1 as the multi-user operating system WinFrame in 1995. Microsoftlicensed this technology back from Citrix and implemented it into Windows NT 4.0 Terminal Server Edition, under aproject codenamed "Hydra". Windows NT then became the basis of Windows 2000 and Windows XP. As of 2011[1]Microsoft Windows systems support graphical terminals via the Remote Desktop Services component.

The term thin client was coined in 1993 by Tim Negris, VP of Server Marketing at Oracle Corp., while working withcompany founder Larry Ellison on the launch of Oracle 7. At the time, Oracle wished to differentiate their serveroriented software from Microsoft's desktop oriented products. Ellison subsequently popularized Negris's buzzwordwith frequent use in his speeches and interviews about Oracle products.

Size comparison - traditional desktop PC vs ClientronU700

The term stuck for several reasons. The earlier term "graphicalterminal" had been chosen to distinguish such terminals fromtext-based terminals, and thus put the emphasis heavily ongraphics - which became obsolete as a distinguishingcharacteristic in the 1990s as text-only physical terminalsthemselves became obsolete, and text-only computer systems (afew of which existed in the 1980s) were no longer manufactured.The term "thin client" also conveys better what was then viewed asthe fundamental difference: thin clients can be designed with lessexpensive hardware, because they have reduced computationalworkloads.

By the 2010s, however, thin clients were not the only desktopdevices for general purpose computing that were "thin" - in thesense of having a small form factor and being relativelyinexpensive. The Nettop form factor for desktop PCs wasintroduced, and nettops could run full feature Windows or Linux;tablets and tablet-laptop hybrids had also entered the market.However, while there was now little size difference, thin clients retained some key advantages over thesecompetitors, such as not needing a local drive. However, "thin client" can be a misnomer for slim form factorcomputers using flash memory such as compactflash, SD card, or permanent flash memory as a hard disc substitute.

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Characteristics of thin clients

Single point of failureThe server, in taking on the whole processing load of several clients, forms a single point of failure for those clients.This has both positive and negative aspects. On the one hand, the security threat model for the software becomesmore focused on the servers. The clients do not run the software; therefore, only a small number of computers (theservers) need to be secured at a software level, rather than securing software installed on every single clientcomputer (although client computers may still require physical security and strong authentication, to preventunauthorised access, depending on requirements). On the other hand, any denial of service attack against the serverwill limit the access of many clients. The server software is typically written with virtual machine technology soevery client is isolated and a client crash is easily handled and rebooted. The single point of failure can still exist,however. If the server crashes, data loss is possible.For small networks, this single-point of failure property might be expanded. The hosting server can be integratedwith file servers and print servers relevant to its clients. This can simplify the network and its maintenance, but mightincrease the risk against that server.In practice, redundancy can be provided both in the form of additional connectivity from server to the network aswell as in the servers themselves, using features like RAID, distributed servers (multiple networked serversappearing as one server to the users), clustered filesystems (which allow files to be accessed from multiple servers),VMWare High Availability and Fault Tolerance or Citrix XenApp's load balancing.

Cheap client hardwareWhile the server must be robust enough to handle several client sessions at once, the clients can be assembled frommuch cheaper hardware than that of a fat client. Many clients have minimal RAM, some do not even have a harddrive. This reduces the power consumption of those clients, and makes the system marginally scalable, i.e. it isrelatively cheap to connect additional client terminals. The thin clients usually have a very low total cost ofownership, but the need for a robust server infrastructure offsets some cost savings. Thin clients also generally usevery low power and might not even require cooling fans, but the servers consume high power and almost alwaysrequire an environmentally controlled air conditioned server room.

Client simplicity

Gigabyte TA7 thin client

Since the clients are made from low cost hardware with few moving parts, they canoperate in more hostile environments than conventional computers. However, theyinevitably need a network connection to their server, which must be isolated from suchhostile environments. Since thin clients are cheap, they offer a low risk of theft ingeneral, and are easy to replace if stolen or broken. Since they do not have anycomplicated boot images, the problem of boot image control is centralized to the server.

On the other hand, to achieve this simplicity, thin clients sometimes lag behind thickclients (PC Desktops) in terms of extensibility. For example, if a local software utility orset of device drivers are needed in order to support a locally attached peripheral device(e.g. printer, scanner, biometric security device), the thin client operating system maylack the resources needed to fully integrate the needed dependencies. Modern thin clientsattempt to address this limitation via port mapping or USB redirection software.However, these methods cannot address all use case scenarios for the vast number ofperipheral types being put to use today.

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Slow bitmapped/animated graphicsThin clients tend to be optimized for use with simple lines, curves, and text, which can be rapidly drawn by the clientusing predefined stored procedures and cached bitmap data. In this regard, thin clients work well for basic officeapplications such as spreadsheets, word processing, data entry, and so forth.However, all thin clients suffer performance problems when large areas of the graphics display must be updatedrapidly with high detail bitmap graphics, which may also need to be redrawn several times per second for animationpurposes. In a few cases it may be possible to use a video stream that was already previously compressed such asMPEG or H.264 video, but many graphical programs such photo editors, 3D drawing programs, and animation toolsrequire high detail uncompressed bitmaps to be displayed in order for the software to be used effectively. Graphicsrich 3D games can be completely unusable on a thin client unless the updated screen area is kept very small or theoverall screen resolution is very low, to reduce the amount of data sent to the client.In an attempt to reduce network bandwidth, the server may try to compress high detail bitmaps on the fly beforesending the data to the client, but this adds latency to the client-server communications, and may reduce userinterface responsiveness. Many thin clients offer options to turn off various graphics rich user interface effects inorder to increase performance, such as not showing the contents of a window while dragging or not displaying adesktop background.

Thin client variants

Web-centric thin client

Repurposing a PC as a thin client

The following options allow a PC to be used as a thin client - in some cases, even if ithas no working hard drive: Linux Terminal Server Project Thinstation OpenThinClient AnywhereTS Remote desktop software

Ultra-thin client, Zero client, or ClientlessTraditionally, a thin client ran a full operating system for the purposes of connecting to other computers.[citationneeded] Some thin clients, such as the Sun Ray, use a simpler protocol for communicating display updates, and theseare sometimes called ultra-thin clients or a zero clients,.[2] Their tiny operating systems merely initialize thenetwork, begin the networking protocol, handle display of the server's output, and transmit user input events.[citationneeded] The full desktop is run remotely and the displayed graphics and text are compressed with either a remotedisplay protocol such as PCoIP, or even just a video codec such as VP9 or Daala, and sent to the zero client. Theclient silicon is now much simpler and lower cost[citation needed] as all it requires is a video decoder[citation needed] andbasic I/O.

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RTE clientA Run Time Environment (RTE) client contains task specific applications (e.g. Mozilla Firefox for Internetbrowsing) and only the minimal (often customized) underlying and supporting code (BIOS, firmware, kernel,libraries, plug-ins, etc.) to run only those applications. It contains all and only the code needed to accomplish itsspecific task, thus it is more than a zero client but less than a typical thin client computer. The RTE client does nothave a general purpose operating system - it usually lacks shells (terminal windows), is not designed to be patched(updated online), has minimal connectivity to external resources, and is often found in read-only media (e.g. tamperresistant ROM chips, CD-ROM, etc.). Attempts to inject or run any other applications/processes/threads results incrashing the kernel (system).[citation needed] Due to the need to physically update the device, RTE clients are mostlyfound in stable environments demanding high security.

Web thin clientWeb thin clients only provide a web browser, and rely on web applications to provide general-purpose computingfunctionality. However, note that web applications may use web storage to store some data locally, e.g. for "offlinemode", and they can perform significant processing tasks as well. Rich Internet Applications for instance may crossthe boundary, and HTML5 Web Applications can leverage browsers as run-time environments through the use of acache manifest or so called "packaged apps" (in Firefox OS and Chrome).Examples of web thin clients include Chromebooks and Chromeboxes (which run Chrome OS) and phones runningFirefox OS.Chromebooks and Chromeboxes also have the capability of remote desktop using the free Chrome Remote Desktopbrowser extension, which means, other than being a web thin client, they can also be used as an ultra-thin client (seeabove) to access PC or Mac applications that do not run on the Chromebook directly. Indeed, they can be used as aweb thin client and an ultra-thin-client simultaneously, with the user switching between web browser and PC or Macapplication windows with a click.Chromebooks are also able to store user documents locally - though, with the exception of media files (which have adedicated player application to play them), all such files can only be opened and processed with web applications,since traditional desktop applications cannot be installed in Chrome OS.Web thin clients are similar to RTE clients, but unlike first-generation RTE clients the operating system can typicallybe updated. Chrome OS, for example, automatically updates itself if its update servers (which are hosted by Google)are not blocked by a firewall - while still being tamper-resistant due to its use of Trusted Computing technologies.

Applications as thin clientsThe notion of a thin client extends indirectly to any clientserver architecture, in which case, a thin client applicationis simply one which relies on its server to process most or all of its business logic. This idiom is relatively commonfor computer security reasons. A client obviously cannot be trusted with the logic that determines how trustworthythey are, because an adversary can circumvent that logic.However, in web development in particular, many client applications are becoming fatter. This is due to the adoptionof heavily client-side technologies like Flash and Ajax, which are themselves strongly driven by the highlyinteractive nature of Web 2.0 applications.

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List of protocols used by thin clientsThis list is incomplete; you can help by expanding it [1].

Appliance Link Protocol Citrix ICA Linux Terminal Server Project NFS PCoIP various video codecs such as VP9 Remote Desktop Protocol Remote Graphics Software Secure Shell or SSH, an encrypted replacement for telnet. Virtual Network Computing X11, central to traditional Unix graphical windowing systems XML, HTML, or JSON over HTTP (Ajax) XDMCP

References[1] http:/ / en. wikipedia. org/ w/ index. php?title=Thin_client& action=edit[2] t310 Zero Client (http:/ / www8. hp. com/ us/ en/ campaigns/ thin-client-solutions/ zero-clients. html)

{{ Thinava (http:/ / www. Thinava. com)}}

Article Sources and Contributors 7

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Image Sources, Licenses and ContributorsImage:Thin clients.png Source: http://en.wikipedia.org/w/index.php?title=File:Thin_clients.png License: Creative Commons Attribution 3.0 Contributors: User:Wing045Image:PCExpanion.jpg Source: http://en.wikipedia.org/w/index.php?title=File:PCExpanion.jpg License: Public Domain Contributors: Raysonho @ Open Grid Scheduler / Grid EngineImage:Aleutia E3 Medium Client in Hand.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Aleutia_E3_Medium_Client_in_Hand.jpg License: Public Domain Contributors: Aleutia(talk). Original uploader was Aleutia at en.wikipediaImage:Samsung Chromebox.JPG Source: http://en.wikipedia.org/w/index.php?title=File:Samsung_Chromebox.JPG License: Creative Commons Attribution-Sharealike 3.0 Contributors:User:Barte1Image:ClientronU700.jpg Source: http://en.wikipedia.org/w/index.php?title=File:ClientronU700.jpg License: Creative Commons Attribution-Sharealike 3.0 Contributors: DjjajahImage:Gigabyte TA7.JPG Source: http://en.wikipedia.org/w/index.php?title=File:Gigabyte_TA7.JPG License: Creative Commons Attribution 2.5 Contributors: Craig SpurrierImage:Arbyte nettop.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Arbyte_nettop.jpg License: Creative Commons Attribution-Sharealike 3.0 Contributors: SergeyAK

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Thin clientHistory Characteristics of thin clients Single point of failure Cheap client hardware Client simplicity Slow bitmapped/animated graphics

Thin client variants Repurposing a PC as a thin clientUltra-thin client, Zero client, or Clientless RTE client Web thin client Applications as thin clients

List of protocols used by thin clients References

License