Thin Client

Thin Client is a term which refers to an alternative to a traditional PC which boasts a smaller footprint on the desk (sometimes none!), far less power consumption, no moving parts so lasts longer, highly secure because no software can be installed by the user - and is far less to purchase than a PC. But this is not the complete picture ...

Some historical context
The advent of the PC in 1981 brought a revolution to the ways users could harness computing power. Previously (since the 1960s) software ran on a Mainframe and users logged in to this via a terminal. This system worked well for enterprise wide applications like for example, warehouse management. The terminal consisted of a keyboard and a basic screen (often with only monochrome display which was text only) but had no processing power of its own. Users had no ability to personalise their terminal and the IT Department* tightly controlled which users could access the various parts of the system. For instance, Purchasing might be able to place orders and update stock, whilst Sales might be able to simply view stock of the items they were selling and get price information. This computing model is "server centric" - with tight control of all computing resources from the centre of the system, the server.

*IT Departments did not really exist in the early days of the PC. The department which controlled the servers and the applications they ran were called MIS (Management Information Systems). At this stage, their remit often did not include PC's and they were quite happy for users to buy them out of their own department budgets.

The PC turned this computing model on its head. Now, a system on your desk could run a multitude of applications such as wordprocessor or spreadsheet and the user had control over the computing environment in which they worked. Users loved the freedom which PC's brought as well as the dramatic improvements in productivity as new applications came along. This computing model is "client centric" - meaning control of the computing resource is with the end user - the client.

Things started to get interesting when PC's got attached to networks towards the end of the 1980s. All of a sudden, users could share data and shortly afterwards the first e-mail applications started to appear. The practice of writing, printing and posting "memos" around the company disappeared with messages now being sent electronically. Electronic data generated by PC's became more critical to business operations and so it became important for someone to control the protection of this data both in terms of backups (protection against loss) and security (keeping data from getting into the wrong hands). The experts in this field typically were MIS and so their role broadened, often to their dismay, to include managing PCs.

Interestingly, one of the applications that could be run on a PC was "terminal emulation". Instead of using the traditional dumb terminals to access the Mainframe - now PC's could do this. Why have two sets of keyboards and monitors on your desk when one could do the job of both?

PC's could also connect to Unix based servers over the network. A computing model called client/ server evolved whereby software running on the PC provided the front end of the solution. This is where users interacted with the system - perhaps entering sales order information for example. The software on the PC then interacted with complimentary software on the server which processed and stored the data. This allowed for a much more interactive user experience - often with a graphical user interface as opposed to text only on terminals. This computing model persists to the present day and is sometimes used on Industry Standard servers too. A common example is Microsoft Outlook - which is a PC based application where users manage e-mail, calendar, tasks, contacts etc. On the server end, the complimentary solution is called Microsoft Exchange. This is a central depository for emails, calendars etc - and is responsible for the actual sending of emails.

If we wind forwards to the present day, PC's have proliferated enormously with one (or sometimes more) on every person's desk. IT departments have evolved too and typically have responsibility for everything connected to the network including PC's, laptops, printers, servers, storage etc.

The cost of managing PC's
Protecting data on PC's and laptops (security and backup) is still a major challenge but a range of technologies and tools have emerged which help IT departments control the PC environment whilst still allowing end users a degree of freedom. Even so, the cost burden of managing high numbers of PCs is extremely significant: keeping records of where they are (asset management), tracking what software versions are deployed and licenced legally (Software Asset Management), deploying new applications when needed, fixing software issues created by users "tinkering", anti virus and security measures, data backup - the list is enormous.

These were not really issues when users only accessed a dumb terminal to a mainframe - and so a couple of new computing models have developed which are server centric yet still provide users with the functionality they have grown to expect from their PC's. The first is "Server Based Computing" which we will cover here and the second is "Virtual Desktop Infrastructure" which has its own section. Both of these also relate to a technology called "Thin Client" - which is an option available for the user's desk instead of PC.

Server Based Computing
As PC's became networked and their underlying processing power evolved, the concept of an Industry Standard server came into being. These systems were like PCs on steroids and had a high end processor, a large chassis which could house multiple hard disks, RAID controllers and other features like dual power supplies and multiple network cards. In 1996, Microsoft launched Windows NT 4 as an operating system designed specifically for servers and high end PC Workstations. It was not the first version of NT, but for the first time it was taken seriously as a contender for running mission critical applications (versus Mainframe or Unix based servers).

One of the features built into NT 4 was a program called Terminal Server which used technology licenced from a firm called Citrix. This allowed users to attach to the server via a PC over the network and remotely run application sessions. In other words, applications like MS Word, could now be run on the server - the PC acting essentially as a terminal - providing keyboard and mouse inputs and the screen showing the status of the application being run on the server. The remote access part of the solution was provided through a protocol called RDP (Remote Desktop Protocol). From the user's perspective, MS Word in our example, appeared to be running on their PC, but it was actually running on the server. Terminal Services allows for many users to be running the same application on the server, each user experiencing it as if it was running on their own PC.

The advantage of this approach is that all application data resides on the server. The server is firmly under the control of the IT department - so data backup and security can be tightly managed. It also means that the software required on the PC is greatly reduced and simplified meaning the costs for managing these systems is greatly reduced. This setup is not restricted to one application, in fact the whole suite of applications users need can be run in this way. (Some exceptions have included applications which require graphics or multimedia capability, or specialised connectivity to devices connected to the PC's).

Thin Client
The functionality for Terminal Services built into Windows NT was a little restricted. Citrix took the concept further, adding enhanced functionality. Citrix have since built a reputation for innovative "server based computing" solutions which have evolved alongside the basic Terminal Services in Windows. This technology really comes into its own when PC's get replaced by "terminals". The server is doing all the necessary application processing, so why would you need to pay for a high end PC when all that is needed is a device which provides keyboard and mouse input and a display. With the demise of the mainframe, most manufacturers of Terminals disappeared. A notable exception was a company called Wyse - who now boast leading market share in the new terminal market - connecting to Industry Standard servers. The name "terminal" harped back to the mainframe era - so a newer name was needed within the fashion conscious world of IT. "Thin Client" is the newer term which has stuck ever since.

Thin Clients are available from a range of vendors many of which have emerged as a result of the new wave of Windows Server based computing environments. Unix servers also provide a platform for server based computing. The Thin Clients themselves typically support a range of remote access protocols (RDP is not the only one) and so can be used for a wide range of applications.

Citrix found great success in organisations where many users had need for basic office productivity applications or access to company wide systems like our earlier example of a warehouse management system (historically run on a mainframe but now with options to run on Windows or Unix based servers). The death of the PC was heralded - but exaggerated. Thin Clients coupled with "server based computing" at the backend promise massive savings in terms of desktop systems management, power consumption, purchase cost, software licencing and more. However, the Achilles heel of Thin Clients is that applications which require graphics, multimedia and device connectivity don't lend themselves to this approach. RDP was never really designed to cope with these demands and so third party vendors (like Citrix, Wyse, Teradici and others) have developed enhancements or alternatives to the basic protocol.

The other Thin Client challenge is that it relies on a high performance network connection and highly performant servers. The attraction of cheap, longlasting and easy to manage Thin Clients is obvious - but only the tip of the iceburg. All the application processing has to happen somewhere - so the costs of many "Fat Client" PCs are actually just being moved into the server and network infrastructure. Cost savings alone may not justify such a big architectural change.

Mobile workers have obvious network challenges when mobile meaning Thin Client is not really an option here.

One last factor caught out some early adopters of this technology. Unless great care is taken in designing the backend infrastructure including the servers, storage and networking - it is quite possible for the responsiveness of applications to be reduced in ways which can be very annoying to users. Anyone who has experienced jerky mouse syndrome or excessive "hourglass" symbols on the screen will understand. Server based computing users can suffer these a lot.

Some vendors have focussed on the networking aspects of Thin Client. A class of product called a "connection broker" has developed which provides intelligent, high speed, low latency connections of thin clients to the servers at the backend. These can provide convincing results and in many cases - tackle the limitations around video, multimedia and device connectivity. However, broker technology does add a layer of complexity and cost.

Many of these early problems now have very solid fixes in place - but even if you are looking at server based computing solutions today - do not underestimate the importance of ensuring a great end user experience. Pilot and test before you deploy!

Application Streaming
One of the ways to overcome the original shortfalls of server based computing is to allow the client device some processing power. The ability to install applications is not an option because that immediately negates the advantages of the Thin Client model. However, allowing the client device to have some graphics processing capability, for example, can be very useful. So for web browsing, some client devices have an onboard video player (a bit like Microsoft Media Player) meaning the task of playing back a video can happen on the client device. It is also possible to "Stream" applications, like our MS Word example, where some of the processing can happen at the client. So not all Thin Clients are equal. In fact they range from Thin to Tubby- depending on how the infrastructure as a whole is designed.

Application Virtualisation
For situations where client mobility is important, it is actually possible to stream the whole of an application onto the client device. Once done, the client device can be disconnected from the server but still run the application. This is Application Virtualisation. Clearly in this situation, a true Thin Client would not have the processing power to run the software but for mobile users, the device of choice would be a laptop. It is important to note that the application is not installed on the laptop. It is virtualised meaning that it is encapsulated in its own software bubble (in fact just a group of files) which can be transported to any computing device (security policies set by IT will probably restrict this). The data in use by the application (in our example Word documents) will now be out of synch with the files on the network. So when the laptop is next connected, files get re-synchronised.

Virtual Desktop
An even more recent technology to emerge is desktop virtualisation. Here, the whole image of the user's PC including data, applications (including operating system) and profiles - jointly called a virtual machine, is run on a server and remotely accessed via a Thin Client (or physical PC). This is more fully explained in the Desktop Virtualisation page. This approach has caused a resurgence in interest in Thin Client solutions - but do not expect "the death of the PC" anytime soon.

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