Recently I've run across companies still running Exchange 4.0 of all things, but the real problem (from Microsoft's point of view, but also objectively in a sense) is NT4. Corporate America is still running a lot of NT4, especially as domain controllers.
Who at this point would bother maintaining large numbers of NT4 servers? A large NT4 enterprise requires huge amounts of babysitting. Servers need to be rebooted every now and then for one thing, a problem that basically goes away in Windows 2000.
Two and a half years since Windows 2000 shipped, running an NT4 enterprise is like keeping your 1979 Dodge in spite of the rattling, the lousy mileage, and the blue smoke because it still runs.
Unlike your Dodge, NT4 won't break down in on a deserted country road in the rain, but if you're still tooling about with NT4, something pretty bad is around the corner. You can't even buy it anymore except through a VAR, and that channel will close on July 1, 2003.
On January 1 of next year, Microsoft support will begin to wither away. A year later most support will be gone and they may even stop providing security fixes. A year after that--just two and a half years from now--even online support will be gone. Nobody's going to stop you from running Microsoft products that aren't supported or available for sale, but is that such a good idea?
And why have you been avoiding upgrading your operating systems? (I don't think anyone can reasonably claim that Windows 2000 would not perform just as well or better than NT4.) There are two major reasons with some merit: First, upgrades like this are expensive, time-consuming, and trouble-prone. Second, moving from NT4 to Windows 2000 for your domain controllers means adopting Active Directory.
Most people like the idea of having Active Directory, but a lot you would like to have six-pack abs too, right? It's the considerable amount of work required to get to AD that makes it worth avoiding. Instead, you've been driving your NT4 clunker all these years, even though it barely passes inspection.
When the time comes, whether you buy into Microsoft's subscriptions or not (the subscription plan is only one of five purchase alternatives in the new licensing system), you're probably going to upgrade to the current version of Windows, because that's the only way you can get Premier Support. Combine this with the fact that Microsoft will retire support for NT4 along with the product and there's a real third-party opportunity for a company that can provide credible support for NT4.
That leaves you with two alternatives: Shape up or ship out. Shaping up means upgrading, and since you're probably going to put this off as long as possible you may end up having to upgrade to Windows .Net Server.
Shipping out means dumping Microsoft and taking your business elsewhere, which you always have the power to do. The least disruptive way to ship out would be to switch your NT4 domains to Samba running on Unix or a variant, most prominently Linux. But as good as it may be, Samba's not a plug-in replacement for an NT4 domain. For example, it doesn't support trust relationships across domains, and if you've got a large NT4 network you probably have trust relationships.
So things are coming to a head, and you've got decisions to make. Whichever way you go--either caving in to Microsoft and upgrading or moving away from Microsoft to alternatives--will involve large costs as well as benefits. But you're going to choose, one way or another.
NT4 is faster than 2000 on old computers. Of course, any computer being used as a server nowadays is probably beyond that threshold. But on the workstation side, a user on a P-166 laptop with 80MB memory has good reason to run NT4. It'll run pretty snappy on that system while 2000's memory demands and IE integration will slow it to a crawl. Some non-profits in particular still have old machines like that.