The 795 has 8TB of main memory and uses eight processor "books," as IBM calls them, each with four Power7 processors. The chips each have eight processor cores, up from two on the Power6, and IBM says the new processors are compatible with Power6-based servers. That means customers can slide Power7 books into an existing Power 695 chassis without any other upgrades required, Sibley said.

IBM is launching the systems into a soft market. Unix server sales have been in decline, with revenue dropping 22 percent between 2008 and 2009, to $13.1 billion, according to IDC. The analyst company expects the market to pick up slightly this year and next.

IBM has been doing better than its rivals in those poor conditions. It sold the most Unix gear in each of the last three years, according to IDC, expanding its share of revenue to 40.3 percent in 2009, compared to 26.2 percent for HP and 25.3 percent for Sun.

The new systems could strengthen its position further. "On a hardware basis, it's pretty clear IBM is in the lead in raw performance," according to Dan Olds, principal analyst at Gabriel Consulting.

Still, IBM's growth came in a period of turmoil for its rivals, said IDC analyst Jean Bozman. HP has been transitioning customers from its PA-RISC chip to Intel's Itanium processor, and Sun's future was clouded for a long time during talk of an acquisition.