We don't got to show you no steenkin' Windows 9!

[AnotherFairportfan]

[ActionKermit]

The explanation I've heard for why Microsoft skipped Windows 9 is that there's a huge amount of legacy code to see whether the version number starts with "9" and then executes functionality that's specific to Windows 95 or 98. That would cause those pieces of software to break on the new operating system, and there's so much of it that asking their customers to fix all that would impose a huge maintenance cost. So they sidestepped the problem by calling the new one 10.

[Warrl]

The only F-21 I can find is an Israeli design, based on the French Mirage fighter.Its primary role is ground-attack aircraft but it can also function as a fighter. A total of 212 were built, of which 12 were leased to the US Navy and 13 to the US Marine Corps. The aircraft was also sold to Colombia, Ecuador, and Sri Lanka (sales were limited because the aircraft used a US-designed engine and therefore, under the agreement by which Israel licensed the design, subject to US export controls).

The USMC should not have sent their F-21s back when they did. They used the aircraft in training exercises as substitutes for certain Russian fighters, with which they shared two major characteristics: being faster (Mach 2+) and somewhat less nimble than other fighters. When the F-21s were sent back to Israel, the new substitute-Russian fighters did not share those characteristics. I assume the decision was made at some other level, or perhaps was embedded in the lease agreement.

[AnotherFairportfan]

From a friend who was a Windows developer through Vista:

The reason for leaping from Windows 8 to Windows 10 has to do with a whole shitpot of legacy application code from non-MS sources that assumes if the operating system name starts with "Windows 9" it's Windows 95 or Windows 98.  The MS internal code uses the internal OS version, which for Windows 7 was actually version 6.2 if memory serves.  Certainly Windows 2000 was v5;  Windows XP was 5.1, etc. The third party legacy code should have used the same mechanism, but like so many MS features, how to find the OS version is badly documented.  Plus -- like with 7 -- the OS version number and external name don't quite align.