Lord_Majestic - 4:54 pm on Oct 15, 2008 (gmt 0)

It is relatively easy - all you do is implement the API calls of the old OS using the API calls of the new OS

It's not easy at all - look at the amount of effort that it took Wine people to make a release, and Windows is relatively API based - DOS had a lot less APIs and completely different memory management.

if IBM had given away OS/2 version 3 (WARP) they would have killed off Microsoft

Not at all - it never run Windows programs as well as Windows, that killed it despite IBM having access to APIs etc - that just proves the point that maintaining backwards compability is very hard thing to do, however it is very valuable advantage if achieved.