IBM announced its most powerful Unix server to date Tuesday, an update to the System p5 595 that will be based on a new Power6 processor running at up to 5 GHz.

IBM also unveiled an update to its System p5 575 supercomputer that has a more efficient, water-based system to cool the processors. IBM hasn't used water-cooling in its servers since 1995, but it expects to use it increasingly as customers wrestle with a shortage of power to their datacenters.

The new systems, which will be discussed in detail at an IBM event in San Francisco Tuesday, continue a rebranding of IBM's servers that started last week. IBM said then that it was merging its System i and System p server lines into a single Power Systems family that can run IBM's AIX flavor of Unix, Linux or its i5/OS, now called i.

The new high-end machine, called the Power 595, is due for wide availability on May 6. Along with the faster processor it uses a new "point to point" interconnect technology to increase system bandwidth and get the most out of a system's processors, cache memory and main memory. It gives an aggregate memory bandwidth of 1.3 terabytes per second, IBM said.

The Power 595 supports up to 4 terabytes of memory, or twice that of the System p 595. The extra memory is good for handling very large databases, heavy transaction loads or consolidating servers. The system can run up to 254 virtualized partitions using IBM's PowerVM virtualization software.

"This will be the fastest Unix server in the world," said Scott Handy [cq], IBM vice president of worldwide marketing and strategy, citing benchmark tests running SAP applications.

IBM is updating a rebate program for customers who trade in processor cores from Sun Microsystems or Hewlett-Packard for its own, Handy said. It is doubling the rewards for HP users, hoping to win them over as HP prepares to phase out its PA RISC processors in favor of Intel's Itanium.

The Power 575 supercomputer uses a new Hydro-Cluster design developed at IBM's research lab in Zurich. It uses a network of copper pipes that sit just above the processors and carry cold water to them and warm water away.

Water cooling is more efficient than air cooling -- 4,000 times more efficient, according to IBM -- and allowed the company to cram 448 4.7GHz Power6 processor cores in a Power 575 rack. That density would have been impossible using air cooling because customers don't have enough power in their datacenters to run the air conditioning units they would need, Handy said.