The Importance of OS Backwards Compatibility

gbjbaanb writes "Raymond Chen (of ancient Microsoft heritage) has a blog where he describes some of the things he's worked on, as well as oddments of obscure code and design decisions in Windows. Regardless of what anyone thinks of Windows, it is informative and often thought-provoking. Recently, Raymond posted an entry about backwards compatibility, and why it is such a big deal for large corporations. Something that I have read about on Slashdot regularly (where Windows is criticized for bothering with it at all), I thought readers would be interested in exactly why Microsoft spends so much effort on backwards compatibility, and by inference, why it is an important topic for getting Linux adopted by big business."

Comments

billions at stake

[yagu]

There is a bit of a "you rub my back..." going on when Microsoft maintains backwards compatibility. While MS is still the 800-lb Guerrilla, they have an audience with which they collaborate to some degree to make billions of dollars. MS holds the reins, but the team would refuse to pull at all if Microsoft cut them all of at the compatibility pass -- that would guarantee a stampede to find alternatives in OS implementations.

I don't think many are aware how hard Microsoft has to work to maintain compatibility... I once talked with one of the MS engineers -- he said much of the OS code has preamble code to run through a giant "case" statement to accommodate and make allowances for either bad or incorrect coding by outside developers, or bugs in their code that don't execute correctly for the outside software. It's a lot of baggage to carry around, but it's baggage worth billions of dollars.

Interestingly (to me) is I don't think Linux's big task yet is to maintain backwards compatibility with Linux programs (though that would be nice, and seems to mostly be a given anyway), I think the bigger task for Linux is to maintain backwards compatibility with Microsoft programs, specifically legacy Windows software. Unless and until that hurdle is cleared, Linux will always be #2, or #3, etc.

(Sorry for the paragraph of metaphors.)

Two ways

[Bluesman]

Backwards compatibility is important, but there are two ways you can do it.

One is to include all of the old stuff in your new OS, the other is to continue to support the old version, or possibly emulate it on the new version.

It seems that backwards compatibility significantly impedes progress. Why not continue to support the older versions, but separate them from the new stuff? Our computers are fast enough to run Windows 3.1 in a VM, much faster than it would run on the hardware it was designed for.

Better yet, include a copy of the old software in the new one, with a built in emulator designed to run it.

It's important to maintain backwards compatibility, but it's just not a good excuse for bad design decisions in new softare.

Re:Huh?

[TheThiefMaster]

Then why upgrade the machines running the legacy apps / scripts at all? It's not like the older versions of windows don't run fine. Making sure they're not connected to the internet is all you need to do to make them secure, or if that's not viable then heavily restrict their access with a firewall (preferably hardware). After all, why should a weather data sensing and reporting machine (for example) be able to connect to anything except the database it's sending the data to? Why should it be able to get any incoming connections at all? Even running unpatched windows 3.0 it would be safe if set up like that.

Do small in-line hardware firewalls exist? Just with an incoming and outgoing RJ45 socket and a hardware circuit that only allows data through to or from a single ip (or range)? I can see many businesses could use these.

Quite true

[csoto]

This is one of the reasons "Solaris is better than Linux." There are few things that we've deployed on Solaris 2.5 (possibly none, but I won't swear to my memory) that don't also work under Solaris 10. This is a far cry from the Linux 2.4-2.6 headaches we've experienced.