Non-R2 vs R2 versions of Microsoft products [closed]

From a technical point. R2 (and R2 - System Center gets one now I hear) are major upgrades without CORE upgrades. I.e. the existing codebase is extended, new features go in.

New versions often have major internal changes.

This is a little like Intel Tick/Tock approach. R2 tries to make the existing code better, while new products allow major rework (like new driver models). Obviously with a huge grey area.

My Product Keys for R2 versions (SQL Server, Windows Server, System Center) do not work with the non-R2 versions, and vice versa. Upgrading SQL Server 2008 to service pack 1 does not require a new product key; upgrading it to SQL Server 2008 R2 does require a new key.

That suggests to me that they are separate products.

You could see the R2 releases as a major minor update or a major minor update to the software (sharing the same codebase), but they are separate versions since keys will not work on both. If you have an active SA (software assurance) subscription for the software, you obviously have the right to upgrade without additional cost.

The product lifecycle is (generally) the same when it comes to mainstream & extended support milestones. This means that (usually) when the 'normal' version goes end-of-life, so does the corresponding 'R2'. There have been exceptions to this, but Microsoft is trying to sync those together due to issues & complaints in the past. For example, 2003 SP2 & 2003 R2 SP2 will both be end-of-support in mid 2015. 2008 SP2 & 2008 R2 SP1 are going end of mainstream support by end of this year (but will have extended support well into the future).