In-Depth

Longhorn: The Base Operating System

The complex model for Longhorn's base operating system illustrates how Microsoft has organized it, as well as where any piece you're interested in fits into the larger view.

The initial round of Longhorn models appears to have been created by geeks, not marketers. That's great, because it lets you see the real organization and underpinnings of Longhorn. On the other hand, marketers are better at simplifying things.

The model for Longhorn's base operating system might leave you a bit overwhelmed by its complexity, but it's important to remember that you're looking at the scale of issues an operating system deals with (see Figure 1). These models illustrate how Microsoft has chosen to break down the problem of organizing an operating system, as well as where any piece you're interested in fits into the larger view.

The base operating system consists of a large number of modules. Some modules are grouped based on the logical services delivered and further categorized as to whether they reside inside or outside (1) the kernel. The kernel is the core of the operating system; in past operating systems, it has generally remained loaded while the operating system is functional. Sections of many logical subsystems, such as UI support and transactions, stretch across the kernel boundary and have portions implemented within and outside the kernel. Core operations such as (2) plug and play, (3) power management, (4) drivers, and (5) process management reside logically in the kernel. At the root of the kernel lies the (6) hardware abstraction layer that ultimately interacts with the CPU to get the job done.

You'll notice that Microsoft has made (7) .NET's Common Language Runtime (CLR) part of the base operating system. This enables deep integration with .NET, and will enable Microsoft itself to use .NET languages in creating technologies built on the base operating system. That's great news for .NET developers. The application deployment engine for Click Once is also part of the base operating system. This is strong evidence of Microsoft's commitment to making it easy to deploy the rich client applications that will be the heart of Longhorn development.

A number of network services, including an (8) Internet firewall, are part of the base operating system, and core protocols are supported by the kernel itself. The networking services and all of the base operating system are the features that Microsoft wants developers to be able to assume "just work." Wrapping so many features into the base operating system allows you to rely on a much simpler development and deployment strategy.

It's not shown in the diagrams, but Microsoft also says it will commit to backward compatibility in Longhorn. You probably don't have much need to run VisiCalc (an old DOS-based spreadsheet), but this compatibility commitment will allow you to move to the exciting world of Longhorn development in steps, while maintaining existing applications built initially for Win32 and older platforms, assuming your client hardware is up to snuff. —Kathleen Dollard

About the Author

Kathleen is a consultant, author, trainer and speaker. She’s been a Microsoft MVP for 10 years and is an active member of the INETA Speaker’s Bureau where she receives high marks for her talks. She wrote "Code Generation in Microsoft .NET" (Apress) and often speaks at industry conferences and local user groups around the U.S. Kathleen is the founder and principal of GenDotNet and continues to research code generation and metadata as well as leveraging new technologies springing forth in .NET 3.5. Her passion is helping programmers be smarter in how they develop and consume the range of new technologies, but at the end of the day, she’s a coder writing applications just like you. Reach her at kathleen@mvps.org.

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