Sun Microsystems has detailed an UltraSparc road map that describes a bright future for server workloads that can make use of multiple processor cores. But Sun's plans may pose challenges for users, especially those looking to upgrade in the next two years.

The vendor's current processor workhorses, the UltraSparc IV and IV+, will be succeeded by what Sun calls its "Rock" chip.

That device will contain up to 16 cores and will be designed for database servers and other applications that require a lot of memory and number-crunching firepower, Sun said.

However, Rock isn't due until the middle of 2008.

Sun hasn't said when it will stop making improvements to the UltraSparc IV+, but next summer the company plans to introduce its so-called Advanced Product Line (APL) servers.

Those systems are being developed with Fujitsu Ltd. and will use a Fujitsu version of UltraSparc called Olympus.

APL will replace Sun's existing Sun Fire servers as well as Fujitsu's UltraSparc-based PrimePower hardware line.

Whether users who need upgrades should buy APL machines or wait for Rock-based systems to appear is "a function of timing," said Marc Tremblay, senior vice president and chief architect in Sun's systems group.

Customers that need an UltraSparc upgrade after next summer will probably buy an APL system if they can't wait another year, he said.

Rock "hits the midrange and high end pretty hard," Tremblay said, referring to Sun's UltraSparc-based systems.

He added that Rock-based hardware won't fully replace the APL line, although he didn't provide details on the applications that might continue to require those systems.

Richard Partridge, an analyst at Ideas International, said Sun users must consider more than just timing in deciding whether to buy APL systems or wait for the Rock-based machines.

Sun is betting that by mid-2008, there will be an adequate number of parallel processing applications that will be able to take advantage of Rock's multicore design, Partridge said.

But it may well turn out that many users will still need to buy the APL hardware if the applications they run can't use a large number of processor cores, he added.

By planning to continue to offer APL as well as Rock-based hardware, Sun is "recognizing that they at least need a fallback plan," Partridge said.

Kenneth Edgecombe, executive director of the High Performance Computing Virtual Laboratory, said he expects software vendors to ensure that their applications can work in multicore environments.

The HPCVL runs a cluster of Sun systems installed at five universities and one college in Ontario to support work being done by about 500 researchers.

Users such as the virtual lab can no longer rely on increases in chip speed alone for performance improvements, said Edgecombe, adding that "The days of getting the single-chip processors that were just getting faster and faster and faster are over."