Today, 13 January, is the day on which Microsoft's Windows 7 passes from mainstream support into extended support.
The milestone is the first on the road to Microsoft pulling the plug on January 14th, 2020.
Windows 7 is a widely-admired version of Windows, as it is more stable than its predecessor Windows Vista and did not try to foist a confusing new UI on the operating system as happened with Windows 8.
At last count, Windows 7 therefore ran on about 55 per cent of the world's PC fleet, well ahead of Windows 8 and 8.1 combined.
All versions of Windows 7 move to extended support today and expire come 2020, save the embedded version which Microsoft's page for support timing says is exempt from obsolescence.
The change from mainstream to extended support means Microsoft won't do free support for Windows 7 as of today. Even those with licences paid up, or signed up to licensing programs, will now be charged for Windows 7 support according to Microsoft's support lifecycle policy. Nor will Redmond consider or implement any new features for Windows 7.
Security patches will continue to flow until 2020.
Cast your mind ahead to that far date: by then it's likely Windows 11 – or whatever Microsoft chooses to call Windows by then – will be upon us.
Much speculation suggests that by 2020 Microsoft will have moved away from big-bang Windows releases. Yet Redmond's lifecycle policy provides gives Microsoft a carrot to dangle – free support with more recent OSes - and a stick with which to cajole users into upgrades and/or new licensing agreements.
Will Redmond be able to put down those cudgels?
You've got either a few months – assuming Windows 10 ships by year's end as planned – or five years to find out. ®