Microsoft has shipped the first beta of its next server software to a select group of testers.

Beta 1 of Longhorn Server, which according to Microsoft will not be called Vista Server, includes the core sub-systems such as the Web service gateway called Windows Communication Foundation (formerly Indigo), and base-level APIs that will let developers and IT shops get a feel for the server.

"What Microsoft is asking is that as you are taking a first look at these low-level systems, now is the time to let us know if the core is correct," said Michael Cherry, an analyst with independent research firm Directions on Microsoft. "As more work moves up the stack into the other features, it is harder to come back and fix [the core] if it is not right."

Cherry says there should be enough functionality in the betas to test basic inter-operability between client and server.

The two operating systems are being developed in tandem, but Longhorn is expected to ship six to 12 months after Vista's target ship date of late 2006.

Eric Rudder, senior vice president in Microsoft's servers and tools division, said at the company's financial analysts meeting last month that Microsoft would ship Community Technical Previews and other betas of Longhorn Server throughout this year. The company did not announce when the first public beta would be available.

Longhorn Server beta 1 was made available to 5,000 testers, including OEMs, hardware manufacturers, system builders, independent software vendors, developers and Microsoft's internal IT organization. Microsoft officials say some customer members of its technology advancement program also received the beta.