Even with the latest service pack releases for the two supported Windows clients, rival operating systems Linux and Mac OS X are still eating away at the install base of Microsoft's proprietary operating system. Concomitantly with the retirement of Bill Gates from his day to day role with the Redmond company, Windows has passes the 1 billion milestone in terms of its global audience. And while Microsoft is indeed gunning for the next five billion users, the fact of the matter is that the share of its client is going down month after month for the benefit of Mac OS X and Linux.

Statistics published by Net Applications reveal that Windows was down to 90.89% at the end of the past month from 91.13% in May 2008. This, while Mac OS X is close to reaching no less than 8% of the operating system market, having jumped to 7.94% in June, up from 7.83% in May. In the past couple of months, Linux accounted for an impressive growth going up from 0.68% all the way to 0.80%. Net Applications continue to place Linux under the 1% market share mark, but the open source operating system is approaching the milestone at a rate that translates into a steady growth tendency.

Responsible for the erosion of Windows' market share is not so much XP, even though it has been dropping like a rock ever since Vista hit, but older Windows operating systems on which Microsoft has already pulled the plug in terms of support. Windows 2000, Windows NT, Windows 98 still hold together over 3% of the operating system market, but are seeing their users switch to alternative solutions from month to month.

Service Pack 3 for XP did nothing to impact the descendant trajectory of the operating system which dropped from 72.12% to 71.20% in the past two months. At the same time, even with Service Pack 1, Vista's growth is still limited under 1% per month and has just hit a share of 16.14% at the end of June, representing approximately 160 million licenses of the operating system sold worldwide.