* "Essentials" included Server 2008 R2 SP1, as it was released several months after SBS 2011 Standard (2008 r2 rtm). SBS 2011 Premium not offered. SQL is now à la carte.
** Version number used during entire beta period was 6.4, but abruptly changed to 10.0 just before release. This is unprecedented.
*** Now split into 2, as not-yet-ready features were pulled, to be worked on & released 2~3 months later as Threshold 2. This practice is also unprecedented.

Note: During the 80s and 90s, OS versions were the same as product names: DOS 1.1, 6.2, Windows 1/2/3, NT3.1/3.5/4.0, etc. Starting from 5.0 it was marketed as "2000" and 5.1 was promoted as "XP" which stands for "Xperience!" with the corresponding MS Office XP (aka 2002). Post-Vista, the trend returned to numeric marketing name, but has nothing to do with the actual version no.

Microsoft Operating System Families

Microsoft Operating System Codenames

NOTES:

The following non-mainstream O.S. editions were excluded from our roster for brevity reasons:

When a specific date is given, it's based on the Official General Availability Date. That is, when it was actually available for sale to general public, not the announcement date, release-to-manufacturing date, or advanced access pilot sites roll-out date.

Microsoft ceased further development of the original consumer (so-called 9x) line of O.S. after the Millennium Edition, and merged it into the business (NT) line starting with XP. They created a reduced and simplified version called the Home Edition.

The NT5, NT5.1 and NT6 nomenclature is NOT official. These "aliases" are commonly known and used to signify the equivalent numeric version numbers, had Microsoft not gone to the "model year" naming convention starting at 2000. These are considered the "real version numbers" as they're used internally at Microsoft, and actually listed in the Help | About screens as VERSION no. followed by BUILD no.  There was never NT1, NT2 or NT3.0. Microsoft started that line with matching version number with consumer Windows 3.1.

Product names listed in quotes are Microsoft internal codenames used during planning and development. Actual product names will be different and have yet to be determined or announced. Blackcomb recent went through a codename change. Longhorn server will be named differently from Vista, just as Windows 2003 Server was named differently from XP.

SEE ALSO

• Platform Generations