IBM has refreshed its eServer pSeries AIX (Unix) server range with faster Power4+ processors and on-demand features.

In keeping with the company's on-demand computing vision, several new hardware and software options are provided.

On/off capacity on-demand memory is offered on the p650, p670 and p690 servers, so that customers can activate processors when needed and turn them off otherwise.

Users can also purchase spare memory capacity, activating it when needed in 4GB increments.

IBM also plans to offer applications such as its DB2 database and Tivoli management software on-demand in the autumn. These will be priced by the day, when the customer turns on temporary capacity.

"In today's challenging economic environment, the customer can't afford to pay for the use of systems that sit idle or do not have the capacity they need to generate revenue during periods of peak demand," said Adalio Sanchez, IBM pSeries general manager.

Integrating Power4+ processors into the high-end eServer pSeries reinforces its commitment to Unix, he added.

IBM has nearly doubled its Unix server worldwide revenue market share from 15.3 to 30.1 per cent since the pSeries launch in October 2000, according to IDC's quarterly server market data.

But while sales are holding up well compared to Hewlett Packard and Sun Microsystems, the overall Unix market is shrinking in favour of Linux.

The p670 will start at £119,000 for a four-way system and the p690 at £307,000 for an eight-way configuration, both using existing 1.5GHz processors. No pricing has yet been issued for fully-configured systems or for the p655.

The p690 and p670 will be available on 30 May, with the p655 due in late July.