IBM has been backing a Linux push on all four of its server lines, though the company has been making the most noise on its xSeries Intel server line, where Linux first took root within Big Blue, and its powerful zSeries mainframe line. In an announcement planned for Wednesday, IBM will push Linux for its iSeries line with a scaled-down version of the argument used for mainframes: several copies of Linux can run on a single iSeries server, letting customers consolidate jobs currently running on several computers. IBM announced in May that its iSeries servers had the ability to run as many as 31 versions of Linux, each on a separate partition. Mainframes, by contrast, can run hundreds of these Linux "virtual machines". Linux software for the iSeries is currently in beta testing from Linux sellers SuSE and TurboLinux, an IBM representative said. Red Hat, the leading Linux seller, has said it plans to support all of IBM's server lines. Among the two dozen companies testing Linux on the iSeries are Insurance Management Solutions Group and Sea Island Resorts of Georgia. The iSeries servers, formerly known as the AS/400 line, use largely the same hardware as the pSeries Unix server line but run IBM's OS/400 operating system and usually are set up in advance to run specific jobs such as maintaining e-commerce sites, managing supplies or accounting. IBM credits Linux for helping to boost its zSeries mainframe line's prospects, with Telia, Winnebago, Banco Mercantil and Korean Airlines among about 100 customers having installed it so far. IBM, which has pledged to spend $1bn developing and promoting Linux this year, sees several advantages in the operating system. For one thing, spreading Linux across its four server lines makes it somewhat easier to write higher-level software such as database programs or e-commerce programs that run on all four servers. For another, it associates IBM with a large new programmer community that might otherwise see IBM as a stodgy old-line company. And backing Linux undermines Sun Microsystems, a direct IBM competitor, as well as Microsoft, a part-time IBM competitor. Find out how the open-source movement is revolutionising the high-tech world at ZDNet UK's Linux Lounge. Have your say instantly, and see what others have said. Click on the TalkBack button and go to the Linux lounge forum Let the editors know what you think in the Mailroom. And read other letters.