Thin clients enter the space age

From versatile desktop terminals to the next generation of mobile phones, today’s thin client technology promises improved...

From versatile desktop terminals to the next generation of mobile phones, today’s thin client technology promises improved reliability and manageability


A thin client is a device with limited processing power and storage. It acts primarily as an interface between user and applications hosted across a LAN/WAN or even the Internet. Unlike a modern desktop PC, there are fewer components within a thin client. The lack of hard disk and complex operating system increases system reliability while reducing cost.

The development of the thin computing model

Although the modern graphical user interfaced terminals (WinTerm) are an improvement, the thin client concept is essentially over two decades old. In the early 1960s, bulky mainframe computers cost millions of pounds a year to install and manage, while applications required thousands of man-hours to develop and proved difficult to implement on more than one architecture. These expensive systems often became computing bureaus where multiple applications and users would be given an allotted amount of computing time or connections for applications or data processing. Each of the major mainframe manufacturers required proprietary terminals from vendors such as RCA, IBM and DG.

This business model of low-powered dumb terminals connecting to powerful servers was the forerunner of the modern thin client model. When, in 1981, IBM unveiled their PC desktop computer, it started the trend towards powerful and versatile desktop computing, as opposed to the powerful mainframes/dumb-terminals of the 1970s.

Popular graphic operating systems such as Windows and MAC-OS further reduced the popularity of text-only terminals with their green or amber displays. Within applications such as CAD and DTP, the dumb terminal was no longer viable, and a wealth of new devices such as scanners, laser printers and sound cards made this new PC technology the preferred choice for the medium-sized businesses.

Today's thin client solutions

The modern thin client has evolved immensely from the terminals of the 1960s. The types of applications and user interfaces now resemble a hybrid of modern desktop PC systems with the reliability of legacy dumb terminals. The two basic types of thin client are Windows terminals and ANSI/Console terminals. The latter are now much less popular and generally connect to older mainframes and Unix systems. These text-only terminals are often used in financial institutions and data processing centres, or wherever older VAX and AS400 systems have been deployed in depth.

The newer and increasingly more popular terminal type is the Windows Terminal. Although not exclusively used with Microsoft Windows, these devices are able to display text, graphics and output audio. The rise in popularity of the WinTerm is mostly due to Citrix's WinFrame - launched in 1995 (now Metaframe) - and Microsoft's NT terminal edition. The combination of these two applications allows NT, Unix and Mainframe software to run on centralised servers with only visual and keyboard information carried over the network to each terminal.

This visual information is carried by a protocol layer, usually over ICA (Citrix) or RDP (mostly Microsoft). Of the two common protocols, Citrix's ICA using Metaframe is by far the most advanced, offering many additional scalability and security features. However, it does add further expense to any thin client solution. Another reason for Metaframe's popularity is the large number of computing environments it supports. As well as all the Microsoft Windows varieties, Version 1.8 also has clients for DOS, Unix (9 Flavours), MAC, Java, ActiveX and the popular Explorer and Netscape browsers.

RDP, on the other hand, is a more open protocol, stemming from the T.120 international communications standard. Microsoft, and thin client vendor, NCD, are both adding extensions to the original RDP specification. These improvements are starting to bring the features offered by RDP into line with the rival ICA protocol. Unfortunately, these advances also make RDP less universally compatible between vendors. Potentially, a VHS versus Betamax standards war could occur which could ultimately render one type of technology obsolete, or conversely develop a new "super" standard with the best of both worlds.

The development of the rival ICA/RDP protocols has also provided multimedia features for thin client systems. Applications complete with video and audio streaming is now commonplace because of these two standards.

Deploying a thin client system is also far removed from the highly proprietary and quirky solution of the past. Modern thin clients use standard Ethernet connections with TCP/IP, while support for IPX/SPX and NETBUI are also available under Metaframe. Modern applications that are best suited to the thin client model include CRMs within call centres, database interaction and simple office applications such as word processing and spreadsheets. With the majority of offices now wired for CAT-5 cabling, attaching a thin client to a LAN is very simple. Centralised servers running NT and NetWare now offer limited support for thin clients, straight out of the box.

Main advantage

The main advantage that thin client manufacturers always stress is total cost of ownership (TCO). The theory is that simple, low-cost terminals offer increased reliability, while having all your applications on a centralised server may also relieve the support burden. Support is crucial. Having to upgrade and support software in an office full of desktop PCs is a constant worry for IT departments. Thin clients allow centralised upgrades and support.

Security again is another area where this technology offers many significant advantages. With only a central point of entry for possible viruses or unauthorised software, system administrators can better focus their security efforts. As all information must also pass through a central server for processing, access to sensitive data and unauthorised usage can be monitored or suspended. For end users familiar with the Windows interface and applications, the re-training required to use Windows terminals is minimal.

Main disadvantages

There are several issues that need to be considered when deploying thin client technology. Although the claims of TCO are impressive, thin clients do involve placing all your eggs in one basket to a certain extent, leaving users open to the dreaded total loss of service. With no local processing power, the thin client is totally dependent on both server resources and network availability.

With large installations, having a switched network is essential. Considering that each connected terminal utilising the ICA protocol will commandeer between 14k to 32k per connection, 100Mb Ethernet is often required for large installations. For power users, or those with a requirement for local devices such as scanners, printers or even PDA's, thin clients are much less flexible.

Vendors and manufacturers

The thin client market is still fairly diverse in terms of vendors. Companies such as Wyse and IBM, who dominated the old dumb terminal market, have flourished in the new WinTerm era. These have been joined by a host of traditional PC vendors such as Compaq and Hewlett Packard. Currently, Wyse is still the global leader in the thin client market, with nearly 38 per cent market share (IDC), combined with a considerable share of the OEM market.

A major competitor is NCD, who though having a smaller installed base, are now trying to offer additional value through an innovative software suite aimed at rivalling the dominance of Citrix's Metaframe. On the software front, Citrix are still the largest player in the thin client market, but now that Microsoft has seen the potential for thin client computing, support is now starting to appear in Windows 2000 as standard.

For the thin client market, Windows 2000 may be the catalyst for a greater acceptance of thin clients over "fatter" PCs. The network version of the new 2000 edition has a number of features for smoothly implementing a thin client solution. These include load balancing and remote administration, although these are far less effective than dedicated systems such as Metaframe or ThinPath.

The future of thin clients

The future will see the rise of the thinnest device to date - the mobile phone. At the moment, the modern cellular telephone has most of the requirements to qualify as a thin client: it has a permanent connection to a network; it has high reliability and its services are provided from a central source. Unfortunately, entering and receiving data is still inefficient in its present form factor. Thin client manufacturers and mobile phone companies are all working closely on technologies such as WAP and Bluetooth, and the merging of the cellular telephone and PDAs, coupled with advances in voice control, should see some groundbreaking products emerging over the next few years.

One such innovative new product is Sun Microsystems's SUNRAY 1, although SUN would prefer to forget their previous foray into thin client computing with the ill-fated NC (Network Computer). When in 1996, Scott McNealy (Sun CEO) unveiled the "revolutionary" Java-based NC, he suggested that customers should "take the money you'll save from not having to invest in another mainframe, from not spending on the Year 2000 [problem], and not having to upgrade your desktop PCs, and put it into the Java-computing model". Unfortunately, they didn't. After three years and a handful of sales, this brave product was quietly shelved, leaving Sun several million dollars worse off.

The development work that created Java-station was still useful and Sun's second generation NC, Sunray 1, is potentially a new direction for thin client converts. Sunray is described as the best of Solaris reliability with the popularity of Windows applications such as Exchange, Access and MS Office. The individual, coffee percolator-style appliances attach over a switched network to a Solaris server. This server can run any Solaris application and provide Internet connectivity. Additional NT servers can attach to the Solaris server allowing MS applications to be served straight to each Sunray unit.

Market leader, Wyse Technologies, is also developing several new thin client innovations. In a recent interview with, Dave Mills, European director of marketing outlined the new Thincard concept.

"Thincard is the next evolution of silicon and firmware which will ultimately result in all the functionality of a thin client on a single chip."

Although only in a concept stage, the Thincard looks similar to a PC (formerly PCMCIA) card and contains a microprocessor, video chip, RAM and operating system. To increase connectivity, Thincard will also have USB sockets for a range of peripherals.

Mills continues: "We envisage that within five years IT professionals may well have a Thincard in their wallet, simply plugging the card into a network attached device to access a virtual desktop, anywhere in the world." Already some computer monitor manufacturers are already interested in including Thincard slots for concept displays of the future.

Whether Wyse's Thincard or another rival develops this concept, if used in conjunction with high bandwidth cellular technology (HSCD), it could provide a wireless and highly portable thin client solution unlike anything seen to date.


Thin Client technology is gaining popularity. According to International Data Corporation's August 1999 report, thin client unit shipments in Western Europe had reached 1,800,000. The value of this worldwide market has been estimated to grow to $2.38billion by the year 2001, with an installed base of 14.5 million. The Gartner Group predicts that half of all applications will be run on thin clients by the same year.

This upward trend may be a reaction to the spiralling support costs associated with computing systems. Now that IT departments have to support desktop applications, mobile users, network and intranet services, moving some of their computing operations to a thin model is starting to look very tempting. The speed of technological innovation is also forcing many companies to upgrade hardware every three years, an expense which combined with disruption to business is lessened considerably by thin computing.

Moving from a fat to a thin client model is not a simple task. However, as computing environments upgrade to Windows 2000 or businesses start to explore the ASP markets, thin client computing will become very attractive indeed.

Will Garside

Read more on PC hardware