Steve Ballmer took a few questions yesterday at Mix08 in Las Vegas, and I asked him what Microsoft would do with all Yahoo’s PHP applications if its takeover bid succeeds, especially where they duplicate home-grown applications that are running on ASP.NET.  PHP is deeply embedded into Yahoo’s culture, and Rasmus Lerdorf, who invented PHP, works at Yahoo as Infrastructure Architect.

He gave me a fuller answer than I expected, which is worth quoting in its entirety:

There’s really two different questions. In a number of areas, and I won’t go into specifics, but we will have to make some kind of integration plans after presumably we reach deal and it will be appropriate to talk to the Yahoo guys. We shouldn’t have two of everything. It won’t make sense to have two search services, two advertising services, two mail services, and we’ll have to sort some of that through. Some of that technology undoubtedly will come from Microsoft’s side, and some will undoubtedly come from Yahoo’s side, whatever technology comes, it will also come with an infrastructure that runs it.

You ask what we will do with those PHP applications? I’m sure a bunch of them will be running, at high scale and in production for a long time to come.

I think there’s going to be a lot of innovation in the core infrastructure which we have on Windows today with ASP.NET, and Yahoo have in Linux and PHP today, and over time probably most of the big applications on the Internet will wind up being rebuilt and redone, whether those are ours, or Yahoo’s, or any of the other competitors. But for the foreseeable future we will be a PHP shop, I guess if we own Yahoo, as well as being an ASP.NET shop.

One of the things I love which we got into the new Windows Server, is that we put a lot of attention in to making sure that PHP applications run well on Windows Server. That’s not the current Yahoo environment and I’m not suggesting that we would transition that way, but for those of you who do have PHP skills, we are going to try and make Windows Server the best place to have PHP applications in the future.

It was a good answer, though I’d still expect integration to be difficult. One danger is that post-merger infighting over what gets preserved and what gets scrapped could stifle innovation. Microsoft’s Live platform actually looks increasingly interesting, as we’ve learned here at Mix, and I imagine that some of these teams will be nervous about what will happen to their efforts in Microsoft-Yahoo becomes a reality.