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What is Managed, Unmanaged, Native Code?

Updated:  10/13/2010 09:10 AM
Author:  Shiju Mathews

Status:    Resolved.


With the release of Visual Studio .NET 2003 developers are now willing to consider using the new technology known as managed code.

  • Managed Code Managed Code is what Visual Basic .NET and C# compilers create. It compiles to Intermediate Language (IL), not to machine code that could run directly on your computer. The IL is kept in a file called an assembly, along with metadata that describes the classes, methods, and attributes (such as security requirements) of the code you've created. This assembly is the one-stop-shopping unit of deployment in the .NET world. You copy it to another server to deploy the assembly there—and often that copying is the only step required in the deployment.
    As the assembly runs, the runtime continues to provide services such as security, memory management, threading, and the like. The application is managed by the runtime.

    Managed code runs in the Common Language Runtime. The runtime offers a wide variety of services to your running code. In the usual course of events, it first loads and verifies the assembly to make sure the IL is okay. Then, just in time, as methods are called, the runtime arranges for them to be compiled to machine code suitable for the machine the assembly is running on, and caches this machine code to be used the next time the method is called.

    Visual Basic .NET and C# can produce only managed code. If you're working with those applications, you are making managed code. Visual C++ .NET can produce managed code

  • Unmanaged Code
    It compiled directly to machine code that ran on the machine where you compiled it—and on other machines as long as they had the same chip, or nearly the same. It didn't get services such as security or memory management from an invisible runtime; it got them from the operating system. And importantly, it got them from the operating system explicitly, by asking for them, usually by calling an API provided in the Windows SDK. More recent unmanaged applications got operating system services through COM calls.

  • Native Code

    The phrase native code is used in two contexts. Many people use it as a synonym for unmanaged code: code built with an older tool, or deliberately chosen in Visual C++, that does not run in the runtime, but instead runs natively on the machine. This might be a complete application, or it might be a COM component or DLL that is being called from managed code using COM Interop or PInvoke, two powerful tools that make sure you can use your old code when you move to the new world. I prefer to say .unmanaged code. for this meaning, because it emphasizes that the code does not get the services of the runtime. For example, Code Access Security in managed code prevents code loaded from another server from performing certain destructive actions. If your application calls out to unmanaged code loaded from another server, you won't get that protection.
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