eServer refers to a family of computers produced by IBM.
The family consists of ...
- iSeries -- Midsize (midrange) systems. Formerly AS/400, now i5.
- zSeries -- Mainframe systems, formerly S/390.
- pSeries -- Midsize unix systems, formerly RS/6000.
- xSeries -- PC server type systems.
Check out the [IT Jungle article http://www.itjungle.com/tfh/tfh061305-story03.html] about HP, IBM, Unix, and Windows, tied for the global Server market, according to Gartner and IDC data.