Wall Street's love affair with Linux companies may have ended a long time ago, but the open source operating system's march into the enterprise continues unabated, if slowly. Indeed, while Linux may have lost its lustre for investors, some banks, including CS First Boston and Merrill Lynch, have given it the thumbs-up and have begun replacing old trading systems and servers with Linux-based kit.

But does Linux really amount to anything more than a low-end OS for file, print and Web server applications? It's clearly challenging Windows in such roles - one of the reasons why it became a household name in the mid- to late 1990s - but can it make its mark in more critical enterprise-oriented applications?

In a recent BusinessWeek story, both Dell and HP claimed around 12 per cent of their server customers (ProLiants in HP's case) wanted Linux pre-installed. Sun, meanwhile, claims it's experiencing 25 per cent year-on-year growth in sales of its Linux-based Cobalt server appliances. Positive stats they may be, but these numbers centre on low-cost, 32-bit Intel-based hardware: typical set-ups for office-level file and print servers, not enterprise iron, in other words.

That picture may be misleading, however. Certainly, Dell believes many of its Linux servers are being corralled into clusters to create large-scale number crunching systems for scientific research. IBM too has had some success selling rigs like these to the petrochemical industry for geophysical modelling.

For business computing, Oracle has touted Linux database software for some time, but now it has been joined by IBM and Sybase, and in other application areas, the likes of SAP, BEA and Veritas.

Linux still has some way to go at the high end, but at least it's now able to do make that journey, thanks to the availability of applications like these and to the work its developers to improve the OS' stability and, more importantly, its scalability. Linux could never seriously challenge Unix until these elements were in place.

However, just as Linux becomes more suitable for the enterprise, so too does Windows. Market researcher IDC reckons Linux will show a compound annual growth rate of around 30 per cent over the next few years. Windows' rate may be lower, but it's starting off from a much stronger position. IDC says Windows' share of the server OS market should come close to 50 per cent this year, up from just over 40 per cent in 2001.

This is the real battle, and one Linux seems unlikely to win, given Microsoft's momentum, and its coming push into 64-bit on the back of Itanium and Opteron. The real casualty will be Unix, increasingly relegated to the high end.

But don't forget that Linux is Unix, or at least a member of the family. When Linux gains functional and performance parity with the likes of Solaris and HP-UX, then the non-Microsoft world really will have a Windows alternative that scales from the 32-bit low end right to the 64-bit high end, not one or the other. That will allow Unix vendors to offer the same kind of roots-to-branches server OS as Microsoft can.

Vested interests, such as Sun, with its investment in Solaris, may prefer to portray Linux as a down-market OS, its job to distract Microsoft's attention from the high end. But Microsoft has its eye on the high-end and there are CPU platforms to take it there. It's in everyone but Redmond's interest to makes sure Linux comes along too. ®