Information about Thin Client

A thin client (sometimes also called a lean client) is a client computer or client software in client-server architecture networks which depends primarily on the central server for processing activities, and mainly focuses on conveying input and output between the user and the remote server. In contrast, a thick or fat client does as much processing as possible and passes only data for communications and storage to the server.

Many thin client devices run only web browsers or remote desktop software, meaning that all significant processing occurs on the server. However, recent devices marketed as thin clients can run complete operating systems such as Debian GNU/Linux, qualifying them as diskless nodes or hybrid clients.

As a consequence, the term "thin client", in terms of hardware, has come to encompass any device marketed as, or used as, a thin client in the original definition – even if its actual capabilities are much greater. The term is also sometimes used in an even broader sense which includes diskless nodes.^[1]

Introduction

In designing a client-server application, there is a decision to be made as to which parts of the task should be done on the client, and which on the server. This decision can crucially affect the cost of clients and servers, the robustness and security of the application as a whole, and the flexibility of the design for later modification or porting.

One design question is how application-specific the client software should be. Using standardized client software such as a Web browser or X11 display can save on development costs, since one does not need to develop a custom client—but one must accept the limitations of the standard client.

Depending on the outcome of these decisions we might say that we use either a thin client, a thick/fat client, or a hybrid client.

History

What are now called thin clients were originally called "graphical terminals" when they first appeared, because they were a natural development of the text terminals that had gone before them. (Text terminals are generally not classified as thin clients, because they are from an earlier computing era.)

X terminals were a relatively popular form of graphical terminal in the 1990s.

It is likely that the term "thin client" started to be used instead of "graphical terminal" for the following reasons:

• When thin clients started to come back into vogue, fat clients had long been the norm in most environments. Many IT workers and managers used to working with fat clients such as PCs and Macs would have been unfamiliar with the term "graphical terminal".
• The term "thin client" is more descriptive and relevant than "graphical terminal", in an age in which all desktop computing devices have graphical capabilities.
• As a marketing term, it sounds short and snappy – and also, importantly, it made the technology sound innovative and technologically advanced, even though it was neither – X terminals had been acting as thin clients years before the term was widely used in the IT industry.

Definitions

A thin client (or a lean client) is a network computer without a hard disk drive, which, in client/server applications, is designed to be especially small so that the bulk of the data processing occurs on the server. Usually, the embedded OS in a thin client is stored in a "flash drive" or in a Disk on Module (DOM). The embedded OS in a thin client usually uses some kind of write filter so that the OS and its configuration can only be changed by administrators.

Thin client (computing): A server-centric computing model in which the application software, data, and CPU power resides on a network server rather than on the client computer.

Application program

A thin client as an application program communicates with an application server and relies for most significant elements of its business logic on a separate piece of software, an application server, typically running on a host computer located nearby in a LAN or at a distance on a WAN or MAN.

A thin client does most of its processing on a central server with as little hardware and software as possible at the user's location, and as much as necessary at some centralized managed site.

Other definitions of thin versus thick/fat client application program try to draw the line at whether the deployment of the application requires the installation of additional software at the user site or not. Unfortunately, this is also arguable, since e.g., a browser used for a client application might be part of one client platform, but not the other. So on one platform no additional software installation is required, while another client platform requires it. The only objective definition would seem to be whether the boot image that is normally used to start the user's computer needs to be modified in any way before the client can be used: if not, then, the client is probably thin. Another criterion is related to the management of the thin client device or program. If it can be centrally managed, it is probably thin.

However, a great deal of software is today typically included in a base boot image, specifically to support various user applications, so that it need not be reinstalled on every computer. Often, a departmental boot image is prepared to include applications specific to a department.

User-interface device

A thin client as a device is designed to provide just those functions which are useful for user-interface programs. Often such devices do not include hard disk drives, which may become corrupted by the installation of misbehaved or incompatible software, but instead, in the interests of low maintenance cost and increased mean-time between failures (MTBF) the thin client device will use read-only storage such as a CD-ROM, Network Virtual Drive or flash memory.

Ideally the user will have only a screen, keyboard, a pointing device (if needed) and enough computer to handle display and communications. Numerous companies develop and market these devices.

Device for running a thin client application program

"Thin client" has also been used as a marketing term for computer appliances designed to run thin client software. Wyse Winterms, Neoware's Appliances, Hewlett-Packard HP Compaq t-series, Chip PC Jack PC, saas style Nexterm,X terminal, ClearCube, or web kiosk might be considered thin clients in this sense.

The latest concept in this genre is 'Ultra Thin Client' technology – which takes the 'thin' concept one step further by running the connection client software (Citrix, Windows Terminal Services, telnet etc) directly from the appliance's hardware. This is a marked difference to legacy thin-client hardware architecture which ran an operating system, often Windows CE or Linux between the hardware and connection client software.^[2][3]

Software thin client

Most thin clients are software-only however, and run on standard PC hardware. One example of this software-only thin client is PXES Universal Linux Thin Client, Pilotlinux or Lan Core^[4]. Knoppix is also actively pursuing this market, as is ThinStation. (See also Puppy Linux). Hopnetix is a diskless, network booting thin client software that runs from a Windows server platform, similar to (and potentially licensed from) Neoware Image Manager software. Neoware Image Manager allows a diskless client to stream a complete system disk "on-demand" from a file server. In that perspective, it replaces the IDE or SCSI cable that connects a disk drive to a motherboard by a network protocol and a server that shares virtual disk drives to the client. Another example on the Windows platform is the BeTwin program, which uses extra VGA/DVI graphics ports, or cards, in the host PC plus USB connected keyboards and mice to enable additional workstations.

Examples of thin client and thin client usage

The advocates of both architectures tend to have contentious relationships. In practice, there seems to be little to choose between the two approaches for many applications. A few situations may clearly call for one or the other. Distributed computing projects such as the SETI@home project (whose whole point is to pass off computationally intensive analysis to a large collection of remote computers) are applications that require thick/fat clients. On the other hand multicasting entertainment or educational material to a number of clients might best be done with thin clients since exactly the same material is to be presented at each, providing that the applications do not need to do intensive full-duplex multimedia. Actually, the protocols used between a thin client and its application server (such as X-11, RDP/Remote_Desktop_Protocol or ICA) does not support very well multimedia to be processed on the server and displayed on the client (or getting inputs from the client). For instance, it is in fact impossible to efficiently use Voice_Over_IP(VoIP) using a thin client protocol. When such issues are encountered, the choice of a hybrid client can solve them if such an hybrid client is a diskless node and actually gets its OS and applications from a shared drive, and runs its applications locally (only the drive is remote).

Several companies now sell thin-client laptops that can access internal resources through a Virtual private network so the connection between client and server passes through an encrypted tunnel. This can allow mobile workers to access security-sensitive databases with less risk of lost or compromised data should the laptop be lost or stolen since it has no local storage.

Industrial Thin Client Applications

Since 2006 there has been a growing interest in using Thin Client technology in hazardous areas, such as oil & gas exploration, military mobile use to monitor gen sets and mobile missile installations, and in industry in Zone 1 areas where hardened industrial computers can be prohibitively expensive. Thin Client hardware is easier to seal against environmental hazards and contamination, and can sometimes withstand a wider temperature and vibration level, due to simplified components and lack of moving parts, such as hard drives.

Flash memory is a critical component of these Thin Client terminals. With sufficient Flash (solid-state) memory and the ability to install user firmware and PCI cards, a Thin Client can perform most of the functions that a user would want to perform at these locations, typically called "point-of-attack" or "rig floor". The Thin Client can be equipped with a sealed membrane keypad for operator interface, and I/O (input/output) connectors that allow the Thin Client to be hooked up to a remote location and perform data recording of processes or history of connected device readings, that could be anything from radar to pumps to drilling apparatus.

Industrial Thin Clients typically operate on embedded software systems such as Windows CE.net or Windows XP Embedded Ethernet. Industrial clients typically prefer an OS (operating system) environment in which the Thin Client can easily interface with proprietary firmware (software embedded in memory on a PCB card), and communications often interface with a hosting central computer in a safe environment control room. Ethernet protocol is a preferred network means of interfacing the computers, Thin Clients, and devices being monitored and controlled.



Fiber networks and wireless interface are also popular to enhance versatility in location and installation of Thin Clients. Encryption of data is usually a priority, and wireless options need to rely on a fast Ethernet radio transmitter using 11Mbit/s 2.4 GHz 802.11 output, otherwise data transmission speed and security can be compromised.

Ruggedized Thin Client products therefore enable easy-to-employ industry standard network creation and control at hazardous area zones for less cost and with less risk of failure than full computer systems. In fact, in the first quarter of 2007, mandates have been created by the US Armed Forces to look at Thin Client solutions in all field applications. The military is primarily interested in Thin Client technology in the field due to its improved cost control, more robust construction, less vulnerability to failure and security breaches, lesser weight and greater mobility, and lower incidence of OS failures.

Advantages of thin clients

Obviously, boot image control is much simpler when only thin clients are used – typically a single boot image can accommodate a very wide range of user needs, and be managed centrally, resulting in:

• Lower IT admin costs. Thin clients are managed almost entirely at the server. The hardware has fewer points of failure and the local environment is highly restricted (and often stateless), providing protection from malware.
• Easier to secure. Thin clients can be designed so that no application data ever resides on the client (it is entirely rendered), centralizing malware protection and minimising the risks of physical data theft.
• Lower hardware costs. Thin client hardware is generally cheaper because it does not contain a disk, application memory, or a powerful processor. They also generally have a longer period before requiring an upgrade or becoming obsolete. The total hardware requirements for a thin client system (including both servers and clients) are usually much lower compared to a system with fat clients. One reason for this is that the hardware is better utilized. A CPU in a fat workstation is idle most of the time. With thin clients, memory can be shared. If several users are running the same application, it only needs to be loaded into RAM once with a central server. With fat clients, each workstation must have its own copy of the program in memory.
• Lower Energy Consumption. Dedicated thin client hardware has much lower energy consumption than thick client PCs. This not only reduces energy costs but may mean that in some cases air-conditioning systems are not required or need not be upgraded which can be a significant cost saving and contribute to achieving energy saving targets.
• Easier hardware failure management. If a thin client fails, a replacement can simply be swapped in while the client is repaired; the user is not inconvenienced because their data is not on the client.
• Worthless to most thieves. Thin client hardware, whether dedicated or simply older hardware that has been repurposed via cascading, is useless outside a client-server environment. Burglars interested in computer equipment have a much harder time fencing thin client hardware (and it is less valuable).
• Hostile Environments. Most devices have no moving parts so can be used in dusty environments without the worry of PC fans clogging up and overheating and burning out the PC.
• Less network bandwidth. Since terminal servers typically reside on the same high-speed network backbone as file servers, most network traffic is confined to the server room. In a fat client environment if you open a 10MB document that's 10MB transferred from the file server to your PC. When you save it that's another 10MB from your PC to the server. When you print it the same happens again – another 10MB over the network to your print server and then 10MB onward to the printer. This is highly inefficient. In a thin client environment only mouse movements, keystrokes and screen updates are transmitted from/to the end user. Over efficient protocols such as ICA or NX this can consume as little as 5 kbit/s bandwidth.
• More efficient use of resources. A typical thick-client will be specified to cope with the maximum load the user needs, which can be inefficient at times when it is not utilised. In contrast, thin clients only use the exact amount of resources required by the current task – in a large network, there is a good probability the load from each user will fluctuate in a different cycle to that of another user (i.e. the peaks of one will more than likely correspond, time-wise, to the troughs of another.
• Simple hardware upgrade path. If the peak resource usage is above a pre-defined limit, it is a relatively simple process to add another rack to a blade server (be it power, processing, storage), boosting resources to exactly the amount required. The existing units can be continued in service alongside the new, whereas a thick client model requires an entire desktop unit be replaced, resulting in down-time for the user, and the problem of disposing of the old unit.
• Lower noise. The aforementioned removal of fans reduces the noise produced by the unit. This can create a more pleasant working environment.
• Less Wasted Hardware. Computer hardware is very environmentally damaging. Thin clients can remain in service longer and ultimately produce less surplus computer hardware than an equivalent thick client installation.

Advantages of thick clients

• Fewer server requirements. A thick client server does not require as high a level of performance as a thin client server (since the thick clients themselves do much of the application processing). This may result in cheaper servers although in practice many thin client servers are actually equivalent to file servers in specifications but with additional memory.
• Better multimedia performance. Thick clients have advantages in multimedia-rich applications that would be bandwidth intensive if fully served. For example, thick clients are well suited for video gaming.
• More flexibility. On some operating systems (such as Microsoft Windows) software products are designed for personal computers that have their own local resources. Trying to run this software in a thin client environment can be difficult.
• Suitable for poor network connections. Thin clients can be unusually slow, or very frustrating to use, over a high latency network connection. Moreover, they do not work at all when the network is down. It may be possible to work offline with a thick client, although the network oriented manner in which many people work today means that thick client usage can still be curtailed if the network is down.

Client/Server Protocols

ALP

Appliance Link Protocol is a secure bitmap-based network protocol used by Sun with its Sun Rays.

XML over HTTP

Protocol used by the AJAX model of web applications.

X11

Networking and display protocol available on essentially all Unix variants.

X11 over Secure Shell

Tunneling an X11 session through a ssh session to provide authentication and encryption.

NX technology

Compresses and caches the X11 protocol for better performance.

VNC

Allows for (virtual) desktop sharing.

Citrix ICA

with Citrix Presentation Server

RDP

The default remote desktop access mechanism for MS-Windows

RGS

A client-server software solution developed by HP, to enable remote access to high-performance workstations from a thin-client machine.

HTML over HTTP

Used by a myriad of web applications.

See also

References