Client-Server Technology : Thin Clients

The Role of Client Computers

In client-server technology, a client computer uses its software programs to make requests from server computers over a network. The server computers then process the request and handle delivery back to the client. However, the server may turn into a client if it formulates a service request to forward to another server, say, a database server. Clients and servers connected on a network are also referred to as nodes. Clients can send requests to more than one server. The most common types of clients today are web browsers.

Most typical servers include web servers and database servers. There are several processing characteristics for clients and servers. The client actively initiates requests, making it a ‘master’. Clients usually launch request through GUI’s (Graphic User Interfaces) that interact directly with the user. The client then waits for and receives responses. They usually connect to a small number of servers. Servers, on the other hand, are passive, waiting for client requests. This makes them ‘slaves’ in the client-server communication equation. They accept many requests from many clients at the same time and do usually do not interact with end users. Master/slave models refer to communication protocols in which one machine or software program (‘master’) controls how other machines or software programs (‘slaves’) act. It is the typical protocol model for client-server technology and is also referred to as ‘primary/secondary’.

This article will discuss thin clients and how they affect client-server environments. Thin clients are client computers or client software that rely primarily on the server for all processing activities. It is primarily used only for conveying input and output to the user. Usually, thin clients only run web browsers or remote desktop software. This is administration software that is accessed through GUIs and runs programs locally that are remotely located on a server. This coincides with the current trend toward storing desktop applications and operating systems on the web or other external servers, which allows programs to be accessed only as needed. This removes the need for organizations or individuals to purchase and maintain sophisticated software and hardware, which requires a significant investment.

Components and Functions

In client-server application design, specific processes are assigned to the client and the server. These decisions affect security, cost, and robustness, and porting. Robustness will determine how well the program will recover from errors or operating under conditions of stress. Porting refers to flexibility or the adapting of programs to environments other than the one which they were created for. One of the primary benefits of using thin clients is cost. It is costly to develop application-specific client software. Thin clients use standardized software, like that found in web browsers, as the primary client software and save the money.

Thin clients require four components to function: application programs; user-interface devices; devices for running thin client application programs; and software for thin clients. To communicate with servers, thin clients rely on a separate piece of software located on a server that is located nearby on a LAN (Local Area Network) or more remotely on a WAN (Wide Area Network) or even further away on a MAN (Metropolitan Area Network). Since thin clients locate most of their processing on a server or some other centralized managed site, another criteria for thin client application programs is whether additional software is required on the client/user side to run the program. For a client to be thin, the boot image, which contains the structure and content of a computer storage media, must not require modification to run.

As devices, thin clients provide only those function necessary for interacting with user-interface programs. User interfaces (UIs) function as the point of contact or communication through which users (people) communicate with computer systems. UIs combine menus, screen design, command languages, online help, keyboard commands, and any other programming that can communicate user requests. Primarily, UIs provide for input, in which users can form requests and otherwise manipulate a system or technology, and output, in which the system communicates the effects of the user’s manipulation. In thin clients, user interface devices use ‘read-only memory’ (ROM) in the form of CD-ROMs, network virtual drives, or flash memory.

Read-only storage is memory whose contents cannot be changed. They can, however, be accessed and manipulated to describe a request. In thin clients, UIs usually only possess a screen, a keyboard and a pointing device (mouse or cursor). The client must only have enough power to communicate requests and display responses.

It is important to note that most thin clients are only software running on standard personal computer hardware. Examples of this type of software-only thin client are PXES Universal Thin Client, Pilotlinux, Knoppix, and Puppy Linux.