If some of the companies who were exhibiting at Networld+Interop in Atlanta last week have their way, we could be at the dawn of a new era in computing which moves away from powerful client PCs on the desktop towards a more centralised notion of computing. The case was being made by vendors such as Citrix, NCD and Insignia Solutions, who offer variations of a multi-user version of Windows NT, which turns the operating system into an application server rather than a file and print server. The basic premise behind this technology is that by using a special extended version of Windows NT Advanced Server 3.51 it is possible to deliver full GUI environments from a central server to multiple users on different desktop systems ranging from PC-running DOS or Windows to Macs and UNIX workstations. According to Insignia Solutions' director of business development, Zdravko Podolski, multi-user NT technology finally provides an alternative to running Windows in emulation on Macs and UNIX systems. 'There are two driving forces [behind this technology],' he said. 'There were applications for which emulation does not run fast enough. The second driving force was Windows 95 and NT.' Emulation products such as SoftWindows from Insignia emulated Windows 3.1. The basis of multi-user Windows NT technology lies in a product called WinFrame from Citrix. WinFrame is an extended multi-user version of Windows NT, which allows multiple users to run complete windows environments concurrently on the same server. All that is shipped across the network to the users is the image of their desktop environment as they work. None of the data or applications they work with move from the server to the client - the client essentially becomes a dumb graphical terminal. Using a protocol Citrix developed to ship out these desktop images to the clients called ICA, it is possible to use WinFrame servers across 28.8 dial-up modem connections and achieve responsiveness satisfactory for most regular PC users. Citrix offers ICA clients for PCs running everything from DOS to all flavours of Windows to Macs. NCD and Insignia have both licensed WinFrame from Citrix and have been busy extending it in different ways, and this is where things get interesting and multi-user NT proves itself as a potential environment for the enterprise network. Both companies have extended WinFrame to allow desktop images to be delivered to UNIX workstations using the X protocol. This is specially optimised to the ethernet environment where ICA was designed for low-bandwidth serial connections. In addition, the solutions offered by NCD and Insignia can be used by corporations to leverage heavy investments in UNIX and X technology before the days of robust Windows application servers. The ability of technologies such as WinFrame and WinCenter from NCD and NTrigue from Insignia Solutions to deliver Windows capabilities in a distributed environment has led some to put forward the notion that access to software may soon be available on a pay-per-use basis at both the individual and corporate levels. At the individual level, Internet providers could run multi-user NT servers and their customers could use ICA clients to run applications on those servers. Large corporate network services companies such as CompuServe could offer corporate-scale applications hosting on large servers - or networks or servers - running one or another version of multi-user NT. Mr Podolski points to recurring costs of software upgrades to stay current as a factor which can drive the success of this type of commercial software rental. 'Every year people have to buy tax software,' he said. 'Why can't I do this with my Internet provider? Why can't I go into a copy centre and do my PowerPoint presentation? 'What I also see happening is corporations will have quasi-private networks. It will be your server and your clients and the carrier will be leasing you the lines.' NCD's director of marketing development Jim Fulton thinks that this type of technology will be slow to take off for these sorts of applications. 'People are not going to do this since we have trouble imaging people putting any type of sensitive documents on any type of service provider's systems,' he said. 'It is the issue of control. Even when the technology is there [to do this securely], the psychological issues could very well block it.' This has not stopped some companies from offering these types of services. CompuServe Network Services announced in Atlanta last week that it would be offering Citrix WinFrame application services as part of its remote access services, in which CompuServe installs and manages an NT server for a customer and provides the network connectivity needed for access to the system throughout the enterprise. NCD's Mr Fulton concedes that this may be a reality in a few years, but not as fast as CompuServe and Insignia are suggesting. 'Four or five years from now it could be a different story,' he said. 'We don't see it as a mainstream trend for a few years.'