Spending on servers worldwide rose 4.5% in 2005 to $51.6 billion as companies continued to favour cheaper, lower-end systems, according to research analyst group Gartner.

The results confirm the decade-long shift towards servers based on Intel’s x86 architecture, with processors typically running Windows or Linux.

As a result of the trend, the growth in server shipments was well ahead of the revenue increase, with the number of units sold jumping 12.7% to reach 7.5 million units in the year.

In contrast, shipments of high-end servers based on non-x86 chips, and typically powered by the Unix operating system, declined 5.3% year-on-year, even as revenues increased 0.5%.

IBM and Hewlett-Packard (HP) remain the clear market leaders. Server revenue at IBM rose 3.6% to $16.6 billion, enabling it to sustain a market share of around 32%. HP closed the gap, with revenues up 8.8% to $14.6 billion and a market share of 28%.

But the real contrast was in the next two positions. Revenues at Dell grew 13.3% to $5.5 billion, giving it a 10.5% share, but at Sun Microsystems sales of servers slumped 5.5% to $4.9 billion, cutting Sun’s share to 9.6%.

Gartner’s numbers echoed those of rival analyst firm IDC. However, IDC’s analysis highlighted how server revenues in the fourth quarter were actually down overall for the first time since early 2003. According to IDC, global sales fell 0.2% from the fourth quarter of 2004 to $14.5 billion.