That makes rumours of a Windows 7 Service Pack 2 release date in the middle of 2012 plausible June would be another 16 months.

The Windows 8 release date is still unconfirmed, but we're expecting an announcement and public access to a beta version at Microsoft's Professional Developer conference this September and that argues for the code being finished in the middle of 2012 and on sale before Christmas. Microsoft also tries to get the latest service pack for the previous version of Windows out before the new operating system (the timing means stability and performance fixes that have been developed and tested as part of the next version can be ported back to the previous code base where possible). Windows 7 went on sale in late October 2009 and SP1 came out in late February this year (exactly 16 months later).

Just as new versions of Windows come every two to three years - 'we think somewhere between 24 and 36 months between releases is about right,' says Windows senior VP Steven Sinofsky - service packs come in between, every 12 to 18 months.

Win 7 sp 2