The Microsoft Developer Network is a subscription service for software developers. There are multiple tiers of subscriptions, each higher tier providing more services and products than the lower tier.
In general, most MSDN subscriptions provide access to most of the Windows operating systems for servers and desktops, Visual Studio for programming, SDKs, and SQL Server databases. Periodically, Microsoft will send out refreshed DVDs to the subscribers with the latest versions of these products.
The MSDN website also allows its subscribers to download any of the software they have rights to in their subscription, so they don’t have to wait for the DVDs to be delivered.