.NET Framework

.NET Framework (pronounced as "dot net") is a software framework developed by Microsoft that runs primarily on Microsoft Windows. It includes a large class library named as Framework Class Library (FCL) and provides language interoperability (each language can use code written in other languages) across several programming languages. Programs written for .NET Framework execute in a software environment (in contrast to a hardware environment) named the Common Language Runtime (CLR). The CLR is an application virtual machine that provides services such as security, memory management, and exception handling. As such, computer code written using .NET Framework is called "managed code". FCL and CLR together constitute the .NET Framework.

FCL provides user interface, data access, database connectivity, cryptography, web application development, numeric algorithms, and network communications. Programmers produce software by combining their source code with .NET Framework and other libraries. The framework is intended to be used by most new applications created for the Windows platform. Microsoft also produces an integrated development environment largely for .NET software called Visual Studio.

.NET Framework began as proprietary software, although the firm worked to standardize the software stack almost immediately, even before its first release. Despite the standardization efforts, developers, mainly those in the free and open-source software communities, expressed their unease with the selected terms and the prospects of any free and open-source implementation, especially regarding software patents. Since then, Microsoft has changed .NET development to more closely follow a contemporary model of a community-developed software project, including issuing an update to its patent promising to address the concerns.

.NET Framework led to a family of .NET platforms targeting mobile computing, embedded devices, alternative operating systems, and web browser plug-ins. A reduced version of the framework, .NET Compact Framework, is available on Windows CE platforms, including Windows Mobile devices such as smartphones. .NET Micro Framework is targeted at very resource-constrained embedded devices. Silverlight was available as a web browser plugin. Mono is available for many operating systems and is customized into popular smartphone operating systems (Android and iOS) and game engines. .NET Core targets the Universal Windows Platform (UWP), and cross-platform and cloud computing workloads.

.NET Framework
Microsoft .NET logo
.NET Framework component stack
.NET Framework component stack
Initial releaseFebruary 13, 2002
Stable release
4.8 / April 18, 2019[1]
Operating systemWindows 98 or later, Windows NT 4.0 or later
TypeSoftware framework
LicenseMixed; see § Licensing


Microsoft began developing .NET Framework in the late 1990s, originally under the name of Next Generation Windows Services (NGWS), as part of the .NET strategy. By late 2000, the first beta versions of .NET 1.0 were released.

In August 2000, Microsoft, Hewlett-Packard, and Intel worked to standardize Common Language Infrastructure (CLI) and C#. By December 2001, both were ratified Ecma International (ECMA) standards.[2][3] International Organisation for Standardisation (ISO) followed in April 2003. The current version of ISO standards are ISO/IEC 23271:2012 and ISO/IEC 23270:2006.[4][5]

While Microsoft and their partners hold patents for CLI and C#, ECMA and ISO require that all patents essential to implementation be made available under "reasonable and non-discriminatory terms". The firms agreed to meet these terms, and to make the patents available royalty-free. However, this did not apply for the part of .NET Framework not covered by ECMA-ISO standards, which included Windows Forms, ADO.NET, and ASP.NET. Patents that Microsoft holds in these areas may have deterred non-Microsoft implementations of the full framework.[6]

On October 3, 2007, Microsoft announced that the source code for .NET Framework 3.5 libraries was to become available under the Microsoft Reference Source License (Ms-RSL[a]).[7] The source code repository became available online on January 16, 2008 and included BCL, ASP.NET, ADO.NET, Windows Forms, WPF, and XML. Scott Guthrie of Microsoft promised that LINQ, WCF, and WF libraries were being added.[8]

Microsoft .NET Framework v4.5 logo
Microsoft .NET Framework v4.5 logo

On November 12, 2014, Microsoft announced .NET Core, in an effort to include cross-platform support for .NET, the source release of Microsoft's CoreCLR implementation, source for the "entire […] library stack" for .NET Core, and the adoption of a conventional ("bazaar"-like) open-source development model under the consolation stewardship of the .NET Foundation. Miguel de Icaza describes .NET Core as a "redesigned version of .NET that is based on the simplified version of the class libraries",[9] and Microsoft's Immo Landwerth explained that .NET Core would be "the foundation of all future .NET platforms". At the time of the announcement, the initial release of the .NET Core project had been seeded with a subset of the libraries' source code and coincided with the relicensing of Microsoft's existing .NET reference source away from the restrictions of the Ms-RSL. Landwerth acknowledged the disadvantages of the formerly selected shared license, explaining that it made codename Rotor "a non-starter" as a community-developed open source project because it did not meet the criteria of an Open Source Initiative (OSI) approved license.[10][11][12]

In November 2014, Microsoft also produced an update to its patent grants, which further extends the scope beyond its prior pledges. Prior projects like Mono existed in a legal grey area because Microsoft's earlier grants applied only to the technology in "covered specifications", including strictly the 4th editions each of ECMA-334 and ECMA-335. The new patent promise, however, places no ceiling on the specification version, and even extends to any .NET runtime technologies documented on MSDN that have not been formally specified by the ECMA group, if a project chooses to implement them. This allows Mono and other projects to maintain feature parity with modern .NET features that have been introduced since the 4th edition was published without being at risk of patent litigation over the implementation of those features. The new grant does maintain the restriction that any implementation must maintain minimum compliance with the mandatory parts of the CLI specification.[13]

On March 31, 2016, Microsoft announced at Microsoft Build that they will completely relicense Mono under an MIT License even in scenarios where formerly a commercial license was needed.[14] Microsoft also supplemented its prior patent promise for Mono, stating that they will not assert any "applicable patents" against parties that are "using, selling, offering for sale, importing, or distributing Mono."[15][16] It was announced that the Mono Project was contributed to the .NET Foundation. These developments followed the acquisition of Xamarin, which began in February 2016 and was finished on March 18, 2016.[17]

Microsoft's press release highlights that the cross-platform commitment now allows for a fully open-source, modern server-side .NET stack. Microsoft released the source code for WPF, Windows Forms and WinUI on December 4, 2018.[18]

Release history

Overview of .NET Framework release history[19][20][21]
Development tool Included in Replaces
Windows Windows Server
1.0 1.0 2002-02-13 2009-07-14[22] Visual Studio .NET[23] XP SP1[a] N/A N/A
1.1 1.1 2003-04-24 2015-06-14[22] Visual Studio .NET 2003[23] XP SP2, SP3[b] 2003 1.0[24]
2.0 2.0 2005-11-07 2011-07-12[22] Visual Studio 2005[25] N/A 2003, 2003 R2,[26] 2008 SP2, 2008 R2 SP1 N/A
3.0 2.0 2006-11-06 2011-07-12[22] Expression Blend[27][c] Vista 2008 SP2, 2008 R2 SP1 2.0
3.5 2.0 2007-11-19 2028-10-10[22] Visual Studio 2008[28] 7, 8, 8.1, 10[d] 2008 R2 SP1 2.0, 3.0
4.0 4 2010-04-12 2016-01-12[22] Visual Studio 2010[29] N/A N/A N/A
4.5 4 2012-08-15 2016-01-12[22] Visual Studio 2012[30] 8 2012 4.0
4.5.1 4 2013-10-17 2016-01-12[22] Visual Studio 2013[31] 8.1 2012 R2 4.0, 4.5
4.5.2 4 2014-05-05 N/A[22] N/A N/A N/A 4.0–4.5.1
4.6 4 2015-07-20 N/A[22] Visual Studio 2015[32] 10 v1507 N/A 4.0–4.5.2
4.6.1 4 2015-11-30[33] N/A[22] Visual Studio 2015 Update 1 10 v1511 N/A 4.0–4.6
4.6.2 4 2016-08-02[34] N/A[22] 10 v1607 2016 4.0–4.6.1
4.7 4 2017-04-05[35] N/A[22] Visual Studio 2017 10 v1703 N/A 4.0–4.6.2
4.7.1 4 2017-10-17[36] N/A[22] Visual Studio 2017 10 v1709 2016 v1709 4.0–4.7
4.7.2 4 2018-04-30[37] N/A[22] Visual Studio 2017 10 v1803 2019 4.0–4.7.1
4.8 4 2019-04-18[38] N/A Visual Studio 2019 10 v1903 (Planning) N/A 4.0–4.7.2


a.^ .NET Framework 1.0 is an integral component of Windows XP Media Center Edition and Windows XP Tablet PC Edition. Installation CDs for the Home edition and the Professional edition of Windows XP SP1, SP2 or SP3 come with .NET Framework 1.0 installation packages.[20]
b.^ Installation CDs for the Home edition and the Professional edition of Windows XP SP2 and SP3 come with .NET Framework 1.1 installation packages.[20]
c.^ Expression Blend only covers the Windows Presentation Foundation part of .NET Framework 3.0.
d.^ .NET Framework 3.5 is not automatically installed with Windows 8, 8.1 or 10. It must be installed either from a Windows installation media or from the Internet on demand. Control Panel always attempts the latter.[39]


Overview of the Common Language Infrastructure
Visual overview of the Common Language Infrastructure (CLI)

Common Language Infrastructure

Common Language Infrastructure (CLI) provides a language-neutral platform for application development and execution. By implementing the core aspects of .NET Framework within the scope of CLI, these functions will not be tied to one language but will be available across the many languages supported by the framework.

Common Language Runtime

.NET Framework includes the Common Language Runtime (CLR). It serves as the execution engine of .NET Framework and offers many services such as memory management, type safety, exception handling, garbage collection, security and thread management. All programs written for .NET Framework are executed by the CLR.

Programs written for .NET Framework are compiled into Common Intermediate Language code (CIL), as opposed to being directly compiled into machine code. During execution, an architecture-specific just-in-time compiler (JIT) turns the CIL code into machine code.


Compiled CIL code is stored in CLI assemblies. As mandated by the specification, assemblies are stored in Portable Executable (PE) file format, common on Windows platform for all dynamic-link library (DLL) and executable EXE files. Each assembly consists of one or more files, one of which must contain a manifest bearing the metadata for the assembly. The complete name of an assembly (not to be confused with the file name on disk) contains its simple text name, version number, culture, and public key token. Assemblies are considered equivalent if they share the same complete name.

A private key can also be used by the creator of the assembly for strong naming. The public key token identifies which private key an assembly is signed with. Only the creator of the key pair (typically the person signing the assembly) can sign assemblies that have the same strong name as a prior version assembly, since the creator possesses the private key. Strong naming is required to add assemblies to Global Assembly Cache.

Starting with Visual Studio 2015, .NET Native compilation technology allows for the compilation of .NET code of Universal Windows Platform apps directly to machine code rather than CIL code, but the app must be written in either C# or Visual Basic.NET.[40]

Class library

.NET Framework includes a set of standard class libraries. The class library is organized in a hierarchy of namespaces. Most of the built-in application programming interfaces (APIs) are part of either System.* or Microsoft.* namespaces. These class libraries implement many common functions, such as file reading and writing, graphic rendering, database interaction, and XML document manipulation. The class libraries are available for all CLI compliant languages. The class library is divided into two parts (with no clear boundary): Base Class Library (BCL) and Framework Class Library (FCL).

BCL includes a small subset of the entire class library and is the core set of classes that serve as the basic API of CLR.[41] For .NET Framework most classes considered being part of BCL reside in mscorlib.dll, System.dll and System.Core.dll. BCL classes are available in .NET Framework as well as its alternative implementations including .NET Compact Framework, Microsoft Silverlight, .NET Core and Mono.

FCL is a superset of BCL and refers to the entire class library that ships with .NET Framework. It includes an expanded set of libraries, including the Windows Forms, ASP.NET, and Windows Presentation Foundation (WPF) but also extensions to the base class libraries ADO.NET, Language Integrated Query (LINQ), Windows Communication Foundation (WCF), and Workflow Foundation (WF). FCL is much larger in scope than standard libraries for languages like C++, and comparable in scope to standard libraries of Java.

With the introduction of alternative implementations (e.g., Silverlight), Microsoft introduced the concept of Portable Class Libraries (PCL) allowing a consuming library to run on more than one platform. With the further proliferation of .NET platforms, the PCL approach failed to scale (PCLs are defined intersections of API surface between two or more platforms).[42] As the next evolutionary step of PCL, the .NET Standard Library was created retroactively based on the System.Runtime.dll based APIs found in UWP and Silverlight. New .NET platforms are encouraged to implement a version of the standard library allowing them to re-use extant third-party libraries to run without new versions of them. The .NET Standard Library allows an independent evolution of the library and app model layers within the .NET architecture.[43]

NuGet is the package manager for all .NET platforms. It is used to retrieve third-party libraries into a .NET project with a global library feed at NuGet.org.[44] Private feeds can be maintained separately, e.g., by a build server or a file system directory.

App models

Atop the class libraries, multiple app models are used to create apps. .NET Framework supports Console, Windows Forms, Windows Presentation Foundation, ASP.NET and ASP.NET Core apps by default. Other app models are offered by alternative implementations of the .NET Framework. Console, UWP and ASP.NET Core are available on .NET Core. Mono is used to power Xamarin app models for Android, iOS, and macOS. The retroactive architectural definition of app models showed up in early 2015 and was also applied to prior technologies like Windows Forms or WPF.


Microsoft introduced C++/CLI in Visual Studio 2005, which is a language and means of compiling Visual C++ programs to run within the .NET Framework. Some parts of the C++ program still run within an unmanaged Visual C++ Runtime, while specially modified parts are translated into CIL code and run with the .NET Framework's CLR.

Assemblies compiled using the C++/CLI compiler are termed mixed-mode assemblies, since they contain native and managed code in the same DLL.[45] Such assemblies are more complex to reverse engineer, since .NET decompilers such as .NET Reflector reveal only the managed code.

Design principle


Because computer systems commonly require interaction between newer and older applications, .NET Framework provides means to access functions implemented in newer and older programs that execute outside .NET environment. Access to Component Object Model (COM) components is provided in System.Runtime.InteropServices and System.EnterpriseServices namespaces of the framework. Access to other functions is via Platform Invocation Services (P/Invoke). Access to .NET functions from native applications is via reverse P/Invoke function.

Language independence

.NET Framework introduces a Common Type System (CTS) that defines all possible data types and programming constructs supported by CLR and how they may or may not interact with each other conforming to CLI specification. Because of this feature, .NET Framework supports the exchange of types and object instances between libraries and applications written using any conforming .NET language.

Type safety

CTS and the CLR used in .NET Framework also enforce type safety. This prevents ill-defined casts, wrong method invocations, and memory size issues when accessing an object. This also makes most CLI languages statically typed (with or without type inference). However, starting with .NET Framework 4.0, the Dynamic Language Runtime extended the CLR, allowing dynamically typed languages to be implemented atop the CLI.


While Microsoft has never implemented the full framework on any system except Microsoft Windows, it has engineered the framework to be cross-platform,[46] and implementations are available for other operating systems (see Silverlight and § Alternative implementations). Microsoft submitted the specifications for CLI (which includes the core class libraries, CTS, and CIL),[47][48][49] C#,[50] and C++/CLI[51] to both Ecma International (ECMA) and International Organization for Standardization (ISO), making them available as official standards. This makes it possible for third parties to create compatible implementations of the framework and its languages on other platforms.


.NET Framework has its own security mechanism with two general features: Code Access Security (CAS), and validation and verification. CAS is based on evidence that is associated with a specific assembly. Typically the evidence is the source of the assembly (whether it is installed on the local machine or has been downloaded from the Internet). CAS uses evidence to determine the permissions granted to the code. Other code can demand that calling code be granted a specified permission. The demand causes CLR to perform a call stack walk: every assembly of each method in the call stack is checked for the required permission; if any assembly is not granted the permission a security exception is thrown.

Managed CIL bytecode is easier to reverse-engineer than native code, unless obfuscated.[52][53] .NET decompiler programs enable developers with no reverse-engineering skills to view the source code behind unobfuscated .NET assemblies. In contrast, apps compiled to native machine code are much harder to reverse-engineer, and source code is almost never produced successfully, mainly because of compiler optimizations and lack of reflection.[54] This creates concerns in the business community over the possible loss of trade secrets and the bypassing of license control mechanisms. To mitigate this, Microsoft has included Dotfuscator Community Edition with Visual Studio .NET since 2002.[b] Third-party obfuscation tools are also available from vendors such as VMware, V.i. Labs, Turbo, and Red Gate Software. Method-level encryption tools for .NET code are available from vendors such as SafeNet.

Memory management

CLR frees the developer from the burden of managing memory (allocating and freeing up when done); it handles memory management itself by detecting when memory can be safely freed. Instantiations of .NET types (objects) are allocated from the managed heap; a pool of memory managed by CLR. As long as a reference to an object exists, which may be either direct, or via a graph of objects, the object is considered to be in use. When no reference to an object exists, and it cannot be reached or used, it becomes garbage, eligible for collection.

.NET Framework includes a garbage collector (GC) which runs periodically, on a separate thread from the application's thread, that enumerates all the unusable objects and reclaims the memory allocated to them. It is a non-deterministic, compacting, mark-and-sweep garbage collector. GC runs only when a set amount of memory has been used or there is enough pressure for memory on the system. Since it is not guaranteed when the conditions to reclaim memory are reached, GC runs are non-deterministic. Each .NET application has a set of roots, which are pointers to objects on the managed heap (managed objects). These include references to static objects and objects defined as local variables or method parameters currently in scope, and objects referred to by CPU registers.[55] When GC runs, it pauses the application and then, for each object referred to in the root, it recursively enumerates all the objects reachable from the root objects and marks them as reachable. It uses CLI metadata and reflection to discover the objects encapsulated by an object, and then recursively walk them. It then enumerates all the objects on the heap (which were initially allocated contiguously) using reflection. All objects not marked as reachable are garbage.[55] This is the mark phase.[56] Since the memory held by garbage is of no consequence, it is considered free space. However, this leaves chunks of free space between objects which were initially contiguous. The objects are then compacted together to make free space on the managed heap contiguous again.[55][56] Any reference to an object invalidated by moving the object is updated by GC to reflect the new location.[56] The application is resumed after garbage collection ends. The latest version of .NET framework uses concurrent garbage collection along with user code, making pauses unnoticeable, because it is done in the background.[57]

The garbage collector used by .NET Framework is also generational.[58] Objects are assigned a generation. Newly created objects are tagged Generation 0. Objects that survive one garbage collection are tagged Generation 1. Generation 1 objects that survive another collection are Generation 2. The framework uses up to Generation 2 objects.[58] Higher generation objects are garbage collected less often than lower generation objects. This raises the efficiency of garbage collection, as older objects tend to have longer lifetimes than newer objects.[58] By ignoring older objects in most collection runs, fewer checks and compaction operations are needed in total.[58]


When an application is first launched, the .NET Framework compiles the CIL code into executable code using its just-in-time compiler, and caches the executable program into the .NET Native Image Cache.[59][60] Due to caching, the application launches faster for subsequent launches, although the first launch is usually slower. To speed up the first launch, developers may use the Native Image Generator utility to manually ahead-of-time compile and cache any .NET application.[60]

The garbage collector, which is integrated into the environment, can introduce unanticipated delays of execution over which the developer has little direct control. "In large applications, the number of objects that the garbage collector needs to work with can become very large, which means it can take a very long time to visit and rearrange all of them."[61]

.NET Framework provides support for calling Streaming SIMD Extensions (SSE) via managed code from April 2014 in Visual Studio 2013 Update 2. However, Mono has provided support for SIMD Extensions as of version 2.2 within the Mono.Simd namespace in 2009.[62] Mono's lead developer Miguel de Icaza has expressed hope that this SIMD support will be adopted by CLR's ECMA standard.[63] Streaming SIMD Extensions have been available in x86 CPUs since the introduction of the Pentium III. Some other architectures such as ARM and MIPS also have SIMD extensions. In case the CPU lacks support for those extensions, the instructions are simulated in software.[64]

Alternative implementations

.NET Framework is the predominant implementation of .NET technologies. Other implementations for parts of the framework exist. Although the runtime engine is described by an ECMA-ISO specification, other implementations of it may be encumbered by patent issues; ISO standards may include the disclaimer, "Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights."[65] It is harder to develop alternatives to FCL, which is not described by an open standard and may be subject to copyright restrictions. Also, parts of FCL have Windows-specific functions and behavior, so implementation on non-Windows platforms can be problematic.

Some alternative implementations of parts of the framework are listed here.

  • .NET Micro Framework is a .NET platform for extremely resource-constrained devices. It includes a small version of CLR and supports development in C# (though some developers were able to use VB.NET,[66] albeit with an amount of hacking, and with limited functionalities) and debugging (in an emulator or on hardware), both using Microsoft Visual Studio. It also features a subset of .NET Framework Class Library (about 70 classes with about 420 methods), a GUI framework loosely based on WPF, and additional libraries specific to embedded applications.
  • .NET Core is an alternative Microsoft implementation of the managed code framework; it has similarities with .NET Framework and even shares some API, but is designed based on different sets of principles: It is cross-platform and free and open-source.
  • Mono is an implementation of CLI and FCL, and provides added functions. It is dual-licensed as free and proprietary software. It includes support for ASP.NET, ADO.NET, and Windows Forms libraries for a wide range of architectures and operating systems. It also includes C# and VB.NET compilers.
  • Portable.NET (part of DotGNU) provides an implementation of CLI, parts of FCL, and a C# compiler. It supports a variety of CPUs and operating systems. The project was discontinued, with the last stable release in 2009.
  • Microsoft Shared Source Common Language Infrastructure is a non-free implementation of CLR. However, the last version runs on Windows XP SP2 only, and has not been updated since 2006. Thus, it does not contain all features of version 2.0 of .NET Framework.
  • CrossNet[67] is an implementation of CLI and parts of FCL. It is free software using an open source MIT License.


Microsoft managed code frameworks and their components are licensed as follows:

Component License
.NET Framework (redistributable package) Proprietary software[68]
Reference source code of .NET Framework 4.5 and earlier Microsoft Reference License (Ms-RSL[a])[7][69]
Reference source code of .NET Framework 4.6 MIT License[70]
Mono MIT License[71]
.NET Core
CoreFX, CoreCLR and CLI
MIT License[72]
.NET Micro Framework Apache License 2.0[73]
.NET Compiler Platform (codename "Roslyn") Apache License 2.0[74]
ASP.NET MVC, Web API and Web Pages (Razor) Apache License 2.0[75]
ASP.NET Core Apache License 2.0[76]
ASP.NET Ajax Control Toolkit BSD License[77]
ASP.NET SignalR Apache License 2.0[78]
Entity Framework Apache License 2.0[79]
NuGet Apache License 2.0[80]

See also


  1. ^ a b The license was formerly abbreviated Ms-RL, but Ms-RL now refers to the Microsoft Reciprocal License.
  2. ^ Dotfuscator Community Edition 4.0


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External links

.NET Compact Framework

The Microsoft .NET Compact Framework (.NET CF) is a version of the .NET Framework that is designed to run on resource constrained mobile/embedded devices such as personal digital assistants (PDAs), mobile phones, factory controllers, set-top boxes, etc. The .NET Compact Framework uses some of the same class libraries as the full .NET Framework and also a few libraries designed specifically for mobile devices such as .NET Compact Framework controls. However, the libraries are not exact copies of the .NET Framework; they are scaled down to use less space.

.NET Foundation

The .NET Foundation is an organization incorporated on March 31, 2014, by Microsoft to improve open-source software development and collaboration around the .NET Framework. It was launched at the annual Build 2014 conference held by Microsoft. The foundation is license-agnostic, and projects that come to the foundation are free to choose any open-source license, as defined by the Open Source Initiative (OSI). The foundation uses GitHub to host the open-source projects it manages.Anyone who has contributed to .NET Foundation projects can apply to be a .NET Foundation member. Members can vote in elections for the board of the directors and will preserve the health of the organization.The foundation began with twenty-four projects under its stewardship including .NET Compiler Platform ("Roslyn") and the ASP.NET family of open-source projects, both open-sourced by Microsoft Open Technologies, Inc. (MS Open Tech). Xamarin contributed six of its projects including the open source email libraries MimeKit and MailKit. As of April 2019, it is the steward of 556 projects, including: .NET Core, Entity Framework (EF), Managed Extensibility Framework (MEF), Umbraco, MSBuild, NuGet, Orchard CMS and WorldWide Telescope. Many of these projects are also listed under Outercurve Foundation project galleries.

Its board of directors consists of Scott Hunter (Microsoft), Miguel de Icaza (Microsoft-owned Xamarin), and Oren Novotny.

.NET Framework version history

Microsoft started development on the .NET Framework in the late 1990s originally under the name of Next Generation Windows Services (NGWS). By late 2001 the first beta versions of .NET 1.0 were released. The first version of .NET Framework was released on 13 February 2002, bringing managed code to Windows NT 4.0, 98, 2000, ME and XP.

Since the first version, Microsoft has released nine more upgrades for .NET Framework, seven of which have been released along with a new version of Visual Studio. Two of these upgrades, .NET Framework 2.0 and 4.0, have upgraded Common Language Runtime (CLR). New versions of .NET Framework replace older versions when the CLR version is the same.

The .NET Framework family also includes two versions for mobile or Embedded device use. A reduced version of the framework, the .NET Compact Framework, is available on Windows CE platforms, including Windows Mobile devices such as smartphones. Additionally, the .NET Micro Framework is targeted at severely resource-constrained devices.


ADO.NET is a data access technology from the Microsoft .NET Framework that provides communication between relational and non-relational systems through a common set of components.

ADO.NET is a set of computer software components that programmers can use to access data and data services from a database. It is a part of the base class library that is included with the Microsoft .NET Framework. It is commonly used by programmers to access and modify data stored in relational database systems, though it can also access data in non-relational data sources. ADO.NET is sometimes considered an evolution of ActiveX Data Objects (ADO) technology, but was changed so extensively that it can be considered an entirely new product.


ASP.NET is an open-source server-side web application framework designed for web development to produce dynamic web pages. It was developed by Microsoft to allow programmers to build dynamic web sites, web applications and web services.

It was first released in January 2002 with version 1.0 of the .NET Framework, and is the successor to Microsoft's Active Server Pages (ASP) technology. ASP.NET is built on the Common Language Runtime (CLR), allowing programmers to write ASP.NET code using any supported .NET language. The ASP.NET SOAP extension framework allows ASP.NET components to process SOAP messages.

ASP.NET's successor is ASP.NET Core. It is a re-implementation of ASP.NET as a modular web framework, together with other frameworks like Entity Framework. The new framework uses the new open-source .NET Compiler Platform (codename "Roslyn") and is cross platform. ASP.NET MVC, ASP.NET Web API, and ASP.NET Web Pages (a platform using only Razor pages) have merged into a unified MVC 6.


ASP.NET Core is a free and open-source web framework, and higher performance than ASP.NET, developed by Microsoft and the community. It is a modular framework that runs on both the full .NET Framework, on Windows, and the cross-platform .NET Core. However the expected version ASP.NET Core 3 was announced to work only on .NET Core dropping support of .NET Framework.The framework is a complete rewrite that unites the previously separate ASP.NET MVC and ASP.NET Web API into a single programming model.

Despite being a new framework, built on a new web stack, it does have a high degree of concept compatibility with ASP.NET MVC. ASP.NET Core applications supports side by side versioning in which different applications, running on the same machine, can target different versions of ASP.NET Core. This is not possible with previous versions of ASP.NET.

C Sharp (programming language)

C# (pronounced C sharp) is a general-purpose, multi-paradigm programming language encompassing strong typing, lexically scoped, imperative, declarative, functional, generic, object-oriented (class-based), and component-oriented programming disciplines. It was developed around 2000 by Microsoft within its .NET initiative and later approved as a standard by Ecma (ECMA-334) and ISO (ISO/IEC 23270:2018). C# is one of the programming languages designed for the Common Language Infrastructure.

C# was designed by Anders Hejlsberg, and its development team is currently led by Mads Torgersen. The most recent version is C# 7.3, which was released in 2018 alongside Visual Studio 2017 version 15.7.2.


ClickOnce is a component of Microsoft .NET Framework 2.0 and later, and supports deploying applications made with Windows Forms or Windows Presentation Foundation. It is similar to Java Web Start for the Java Platform or Zero Install for Linux.

Common Language Infrastructure

The Common Language Infrastructure (CLI) is an open specification (technical standard) developed by Microsoft and standardized by ISO and ECMA that describes executable code and a runtime environment that allows multiple high-level languages to be used on different computer platforms without being rewritten for specific architectures. This implies it is platform agnostic. The .NET Framework, .NET Core, Mono, DotGNU and Portable.NET are implementations of the CLI.

Common Language Runtime

The Common Language Runtime (CLR), the virtual machine component of Microsoft's .NET framework, manages the execution of .NET programs. Just-in-time compilation converts the managed code (compiled intermediate language code), into machine instructions which are then executed on the CPU of the computer. The CLR provides additional services including memory management, type safety, exception handling, garbage collection, security and thread management. All programs written for the .NET framework, regardless of programming language, are executed by the CLR. All versions of the .NET framework include CLR. The CLR team was started June 13, 1998.

CLR implements the Virtual Execution System (VES) as defined in the Common Language Infrastructure (CLI) standard, initially developed by Microsoft itself. A public standard defines the Common Language Infrastructure specification.

Extensible Application Markup Language

Extensible Application Markup Language (XAML (listen)) is a declarative XML-based language developed by Microsoft that is used for initializing structured values and objects. It is available under Microsoft's Open Specification Promise. The acronym originally stood for Extensible Avalon Markup Language, Avalon being the code-name for Windows Presentation Foundation (WPF).XAML is used extensively in .NET Framework 3.0 & .NET Framework 4.0 technologies, particularly Windows Presentation Foundation (WPF), Silverlight, Windows Workflow Foundation (WF), Windows Runtime XAML Framework and Windows Store apps. In WPF, XAML forms a user interface markup language to define UI elements, data binding, events, and other features. In WF, workflows can be defined using XAML. XAML can also be used in Silverlight applications, Windows Phone apps and Windows Store apps.

XAML elements map directly to Common Language Runtime object instances, while XAML attributes map to Common Language Runtime properties and events on those objects. XAML files can be created and edited with visual design tools like Microsoft Expression Blend, Microsoft Visual Studio, and the hostable Windows Workflow Foundation visual designer. They can also be created and edited with a standard text editor, a code editor like XAMLPad, or a graphical editor like Vector Architect.

Anything that is created or implemented in XAML can be expressed using a more traditional .NET language, such as C# or Visual Basic .NET. However, a key aspect of the technology is the reduced complexity needed for tools to process XAML, because it is based on XML. Consequently, a variety of products are emerging, particularly in the WPF space, which create XAML-based applications. As XAML is simply based on XML, developers and designers are able to share and edit content freely amongst themselves without requiring compilation. XAML also benefits from being a declarative definition of the UI rather than procedural code to generate it.

Framework Class Library

The Framework Class Library (FCL) is a standard library and Microsoft's .NET Framework implementation of the Standard Libraries as defined in the Common Language Infrastructure. The FCL is a collection of reusable classes, interfaces and value types. The Base Class Library (BCL) is the core of the FCL and provides the most fundamental functionality, which includes classes in namespaces System, System.CodeDom, System.Collections, System.Diagnostics, System.Globalization, System.IO, System.Resources and System.Text.

Microsoft .NET strategy

The Microsoft .NET strategy is a 2000s software development and marketing plan of Microsoft Corporation. Steve Ballmer described it as the company's "most ambitious undertaking since Internet Strategy Day in 1995". In support of this strategy, between 2000 and 2002, Microsoft released ".NET" branded updates to its works, including Visual Studio .NET, Visual Basic .NET, .NET Passport, .NET My Services, .NET Framework, ASP.NET and ADO.NET. A Windows .NET Server was also announced. Microsoft had plans to include Microsoft SQL Server, Microsoft Exchange Server and MSN into this strategy.By 2003, however, the .NET strategy had dwindled into a failed branding campaign because the brand had failed to articulate what Microsoft had in mind in the first place. As such, Windows .NET Server was released under the title of Windows Server 2003. Since then, Visual Studio and .NET Passport have been stripped of ".NET" in their brandings. However, Microsoft and the rest of the computing industry use ".NET" to indicate close association with .NET Framework, e.g. .NET Compiler Platform, .NET Foundation and .NET Reflector.

Parallel Extensions

Parallel Extensions was the development name for a managed concurrency library developed by a collaboration between Microsoft Research and the CLR team at Microsoft. The library was released in version 4.0 of the .NET Framework. It is composed of two parts: Parallel LINQ (PLINQ) and Task Parallel Library (TPL). It also consists of a set of coordination data structures (CDS) – sets of data structures used to synchronize and co-ordinate the execution of concurrent tasks.

Visual Basic .NET

Visual Basic .NET (VB.NET) is a multi-paradigm, object-oriented programming language, implemented on the .NET Framework. Microsoft launched VB.NET in 2002 as the successor to its original Visual Basic language. Although the ".NET" portion of the name was dropped in 2005, this article uses "Visual Basic [.NET]" to refer to all Visual Basic languages released since 2002, in order to distinguish between them and the classic Visual Basic. Along with Visual C#, it is one of the two main languages targeting the .NET framework.

Microsoft's integrated development environment (IDE) for developing in Visual Basic .NET language is Visual Studio. Most Visual Studio editions are commercial; the only exceptions are Visual Studio Express and Visual Studio Community, which are freeware. In addition, the .NET Framework SDK includes a freeware command-line compiler called vbc.exe. Mono also includes a command-line VB.NET compiler.

Windows Communication Foundation

The Windows Communication Foundation (WCF), previously known as Indigo, is a runtime and a set of APIs in the .NET Framework for building connected, service-oriented applications.

Windows Forms

Windows Forms (WinForms) is a graphical (GUI) class library included as a part of Microsoft .NET Framework or Mono Framework, providing a platform to write rich client applications for desktop, laptop, and tablet PCs. While it is seen as a replacement for the earlier and more complex C++ based Microsoft Foundation Class Library, it does not offer a comparable paradigm and only acts as a platform for the user interface tier in a multi-tier solution.At the Microsoft Connect event on December 4, 2018, Microsoft announced releasing Windows Forms as open source project on GitHub. It is released under the MIT License. With this release, Windows Forms has become available for projects targeting the .NET Core framework. However, the framework is still available only on the Windows platform and Mono's incomplete implementation of WinForms remains the only cross-platform implementation.

Windows Presentation Foundation

Windows Presentation Foundation (WPF) is a graphical subsystem by Microsoft for rendering user interfaces in Windows-based applications. WPF, previously known as "Avalon", was initially released as part of .NET Framework 3.0 in 2006. WPF uses DirectX and attempts to provide a consistent programming model for building applications. It separates the user interface from business logic, and resembles similar XML-oriented object models, such as those implemented in XUL and SVG.

WPF employs XAML, an XML-based language, to define and link various interface elements. WPF applications can be deployed as standalone desktop programs or hosted as an embedded object in a website. WPF aims to unify a number of common user interface elements, such as 2D/3D rendering, fixed and adaptive documents, typography, vector graphics, runtime animation, and pre-rendered media. These elements can then be linked and manipulated based on various events, user interactions, and data bindings.

WPF runtime libraries are included with all versions of Microsoft Windows since Windows Vista and Windows Server 2008. Users of Windows XP SP2/SP3 and Windows Server 2003 can optionally install the necessary libraries.Microsoft Silverlight provided functionality that is mostly a subset of WPF to provide embedded web controls comparable to Adobe Flash. 3D runtime rendering had been supported in Silverlight since Silverlight 5.At the Microsoft Connect event on December 4, 2018, Microsoft announced releasing WPF as open source project on GitHub. It is released under the MIT License. Windows Presentation Foundation has become available for projects targeting the .NET Core framework, however, the system is not cross-platform and is still available only on Windows.

Windows Workflow Foundation

Windows Workflow Foundation (WF) is a Microsoft technology that provides an API, an in-process workflow engine, and a rehostable designer to implement long-running processes as workflows within .NET applications. The current version of WF was released as part of the .NET Framework version 4.5 and is referred to as (WF45).A workflow, as defined here, is a series of distinct programming steps or phases. Each step is modeled in WF as an Activity. The .NET Framework provides a library of activities (such as WriteLine, an activity that writes text to the console or other form of output). Custom activities can also be developed for additional functionality. Activities can be assembled visually into workflows using the Workflow Designer, a design surface that runs within Visual Studio. The designer can also be hosted in other applications.

Encapsulating programming functionality into the activities allows the developer to create more manageable applications; each component of execution can be developed as a Common Language Runtime object whose execution will be managed by the workflow runtime.

.NET Framework
Data access
Administration and
Component model
Device drivers
Software factories
Text and multilingual
File systems
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Microsoft Store

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