Lord_Majestic - 3:01 pm on Oct 15, 2008 (gmt 0)

That's 99% due to the fact that Intel 286 CPUs could run 8086 and 8088 code and the 386 could run 286/86/88 code.

That sure helped. But there were and still are plenty of OSes that require recomplies even if the CPU is backwards compatible.

A lot of people underestimate just how hard it is to maintain backwards compatibility - it is very hard, however it is priceless feature of a platform - that's why Intel/Microsoft were such a winning combination, that and low price as well as meaningful (until recently for Microsoft) upgrades. The difference in stability (while maintaining compatability with old software) between MS-DOS 5 -> Windows 3.1 -> Windows 95 -> Windows XP is stagerring - is that not innovation? Maybe Unix had all that for decades, but if it wasn't for Microsoft pushing easy GUI to the masses we'd still have to use Lynx to text browse this forum! :o

that's three years before Windows 3 could run Dos programs

I think you are forgetting that Microsoft was selling OSes well before 1987 - Lotus 1-2-3 for example could run on MS-DOS 3 as well as MS-DOS 5, that made PC architecture (that certainly includes Microsoft OS) priceless - BBC-Micro is just kids stuff :)