[recoiledsnake]

I believe the confusion arises from the use of the term "existing one". That could be construed as referring to NeXT, so it would mean they decided to evolve NeXT by making changes to it over many years, instead of switching to it at once.

If you read "existing one" as Mac OS 9, then that sentence would mean a completely different thing.

[gnaffle]

Well, the text talks about NeXT first, and then suddenly talks about MacOS. When he says that Apple used _some_ of NeXTs software and goes on to talk about the kernel, it seems like he gets it wrong and doesn't really understand what OS X was.

If he had, he would have realized its significance. For instance, I can't recall that he mentions how iOS relates to OSX, and the advantages this brings to Apple. He never mentions that NeXT was compatible with PowerPC and Intel and that Apple would have a working, parallel release running on Intel hardware internally.