Citrix Systems on Wednesday added yet another acquisition to its product line, this time an application that lets administrators set up and configure PCs, servers, and Web services from centrally managed software images.

Citrix is acquiring Waltham, Mass., Ardence for an undisclosed sum. The deal is still subject to the standard regulatory approvals, but is expected to close in early 2007, adding between $15 million and $18 million in new revenue next year for Citrix.

Ardence’s software lets PCs and servers in effect replace their internal disk drive with a disk image file, dubbed a vDisk, on a remote server. As the PC or server goes through its boot operation, the Ardence server associates with it the appropriate vDisk, containing the complete software image (operating system and applications), needed by that computer. The Ardence server can be set up to serve a different vDisk to each client computer or a common vDisk to several or all of them.

Ardence dubs this technique “software streaming” though some observers say that’s imprecise. The Ardence software doesn't actually copy the disk content to the client PC, which is typically what happens with application streaming, according to Brian Madden, president of The Brian Madden Company, Silver Springs, Md., an independent technology consulting firm specialing in Citrix and server-based computing.

Instead, with Ardence, the client computer is mounting, over the network, a disk volume that resides on a remote server. The client computer can actually run without a local hard disk. Madden has a March 2006 report that evaluates using Ardence to manage Citrix servers.

“It’s one of those cases where two technologies [Ardence and Citrix Presentation Server] are an absolutely brilliant fit,” says Madden.

Initially, Madden says, Citrix customers may adopt Ardence to simplify the management of the software images of their backend Citrix servers. But he expects many will start to evaluate how Ardence will support a virtual desktop infrastructure, where PC operating systems run in virtual machines on central servers.

When a user logs on from any client device, that infrastructure provisions a virtual machine for that user, and Ardence would let the software image be mounted over the network from a central server. A new PC or server can be set up by pointing them to the appropriate Ardence vDisk image; an existing computer can be reprovisioned by pointing it to a different vDisk image.