.Net Framework 2.0

The Microsoft .NET Framework is a software component that is a part of Microsoft Windows operating systems. It has a large library of pre-coded solutions to common program requirements, and manages the execution of programs written specifically for the framework. The .NET Framework is a key Microsoft offering, and is intended to be used by most new applications created for the Windows platform.

The pre-coded solutions that form the framework's Base Class Library cover a large range of programming needs in areas including: user interface, data access, database connectivity, cryptography, web application development, numeric algorithms, and network communications. The class library is used by programmers who combine it with their own code to produce applications.

Programs written for the .NET Framework execute in a software environment that manages the program's runtime requirements. This runtime environment, which is also a part of the .NET Framework, is known as the Common Language Runtime (CLR). The CLR provides the appearance of an application virtual machine, so that programmers need not consider the capabilities of the specific CPU that will execute the program. The CLR also provides other important services such as security mechanisms, memory management, and exception handling. The class library and the CLR together compose the .NET Framework.

The .NET Framework is included with Windows Server 2003, Windows Server 2008 and Windows Vista, and can be installed on most older versions of Windows.

Design goals and principal features

Microsoft .NET Framework was designed with several intentions:

Interoperability

Because interaction between new and older applications is commonly required, the .NET Framework provides means to access functionality that is implemented in programs that execute outside the .NET environment. Access to COM components is provided in the System.Runtime.InteropServices and System.EnterpriseServices namespaces of the framework, and access to other functionality is provided using the P/Invoke feature.

Common Runtime Engine

Programming languages on the .NET Framework compile into an intermediate language known as the Common Intermediate Language, or CIL (formerly known as Microsoft Intermediate Language, or MSIL). In Microsoft's implementation, this intermediate language is not interpreted, but rather compiled in a manner known as just-in-time compilation (JIT) into native code. The combination of these concepts is called the Common Language Infrastructure (CLI), a specification; Microsoft's implementation of the CLI is known as the Common Language Runtime (CLR).

Language Independence

The .NET Framework introduces a Common Type System, or CTS. The CTS specification defines all possible datatypes and programming constructs supported by the CLR and how they may or may not interact with each other. Because of this feature, the .NET Framework supports development in multiple programming languages. This is discussed in more detail in Microsoft .NET Languages.

Base Class Library

The Base Class Library (BCL), part of the Framework Class Library (FCL), is a library of functionality available to all languages using the .NET Framework. The BCL provides classes which encapsulate a number of common functions, including file reading and writing, graphic rendering, database interaction and XML document manipulation.

Simplified Deployment

Installation of computer software must be carefully managed to ensure that it does not interfere with previously installed software, and that it conforms to increasingly stringent security requirements. The .NET framework includes design features and tools that help address these requirements.

Security

The design is meant to address some of the vulnerabilities, such as buffer overflows, that have been exploited by malicious software. Additionally, .NET would provide a common security model for all applications.

Portability

A design goal of the .NET Framework is to remain platform agnostic, and thus be cross platform compatible. That is, a program written to use the framework should run without change on any type of system for which the framework is implemented. Microsoft's commercial implementations of the framework cover Windows, Windows CE, and the Xbox 360.[2] In addition, Microsoft submits the specifications for the Common Language Infrastructure (which includes the core class libraries, Common Type System, and the Common Intermediate Language),[3][4][5] and the C# language,[6] and the C++/CLI language[7] to both ECMA and the ISO, making them available as open standards. This makes it possible for third parties to freely implement compatible implementations of the framework and its languages on other platforms.


Architecture

CLI

Main article: Common Language Infrastructure

The core aspects of the .NET framework lie within the Common Language Infrastructure, or CLI. The purpose of the CLI is to provide a language-agnostic platform for application development and execution, including functions for exception handling, garbage collection, security, and interoperability. Microsoft's implementation of the CLI is called the Common Language Runtime, or CLR. The CLR is composed of four primary parts:

* Common Type System (CTS)
* Common Language Specification (CLS)
* Metadata
* Virtual Execution System (VES)

Assemblies

Main article: .NET assembly

The intermediate CIL code is housed in .NET assemblies. As mandated by specification, assemblies are stored in the Portable Executable (PE) format, common on the Windows platform for all DLL and EXE files. The assembly consists of one or more files, but one of these must contain the manifest, which has the metadata for the assembly. The complete name of an assembly (not to be confused with the filename on disk) contains its simple text name, version number, culture and public key token. The public key token is a unique hash generated when the assembly is compiled; thus two assemblies with the same public key token are guaranteed to be identical. A private key can also be specified known only to the creator of the assembly and can be used for strong naming and to guarantee that the assembly is from the same author when a new version of the assembly is compiled (required to add an assembly to the Global Assembly Cache).

Metadata

Main article: .NET metadata

All CIL is Self-Describing through .NET metadata. The CLR checks on metadata to ensure that the correct method is called. Metadata is usually generated by language compilers but developers can create their own metadata through custom attributes. Metadata also contains information about the assembly. Metadata is also used to implement the reflective programming capabilities of .NET Framework.

Class library

Main article: Base Class Library

The Base Class Library, sometimes incorrectly referred to as the Framework Class Library (FCL) (which is a superset including the Microsoft.* namespaces). is a library of classes available to all languages using the .NET Framework. The BCL provides classes which encapsulate a number of common functions such as file reading and writing, graphic rendering, database interaction, XML document manipulation, and so forth. The BCL is much larger than other libraries, but has much more functionality in one package.

Security

.NET has its own security mechanism, with two general features: Code Access Security (CAS), and validation and verification. Code Access Security 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 intranet or Internet). Code Access Security uses evidence to determine the permissions granted to the code. Other code can demand that calling code is granted a specified permission. The demand causes the CLR to perform a call stack walk: every assembly of each method in the call stack is checked for the required permission and if any assembly is not granted the permission then a security exception is thrown.

When an assembly is loaded the CLR performs various tests. Two such tests are validation and verification. During validation the CLR checks that the assembly contains valid metadata and CIL, and it checks that the internal tables are correct. Verification is not so exact. The verification mechanism checks to see if the code does anything that is 'unsafe'. The algorithm used is quite conservative and hence sometimes code that is 'safe' is not verified. Unsafe code will only be executed if the assembly has the 'skip verification' permission, which generally means code that is installed on the local machine.

.NET Framework uses appdomains as a mechanism for isolating code running in a process. Appdomains can be created and code loaded into or unloaded from them independent of other appdomains. This helps increase fault tolerance of the application, as faults or crashes in one appdomain do not affect rest of the application. Appdomains can also be configured independently with different security privileges. This can help increasing security of the application by separating potentially unsafe code. However, the developer has to split the application into subdomains, it is not done by the CLR.

Memory management

The .NET Framework CLR frees the developer from the burden of managing memory (allocating and freeing up when done); instead it does the memory management itself. To this end, the memory allocated to instantiations of .NET types (objects) is done contiguously from the managed heap, a pool of memory managed by the CLR. As long as there exists a reference to an object, which might be either a direct reference to an object or via a graph of objects, the object is considered to be in use by the CLR. When there is no reference to an object, and thus cannot be reached or used, it becomes garbage. However, it still holds on to the memory allocated to it. .NET Framework includes a garbage collector which runs periodically, on a separate thread than the application's thread, that enumerates all the unusable objects and reclaims the memory allocated to them.

The .NET Garbage Collector (GC) is a non-deterministic, compacting, mark-and-sweep garbage collector. The GC runs only when a certain 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 is reached, the GC runs are non-deterministic. Each .NET application has a set of roots , which are a set of pointers maintained by the CLR that point 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, as well as objects referred to by CPU registers. the GC runs, it pauses the application, and for each objects referred to in the root, it recursively enumerates all the objects reachable from the root objects and marks the objects as reachable. It uses .NET 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 and all the objects, not marked as reachable, are garbage. is the mark phase. the memory held by garbage is not of any 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, by using memcpy copy them over to the free space to make them contiguous again. Any reference to an object invalidated by moving the object is updated to reflect the new location by the GC. The application is resumed after the garbage collection is over.

The GC used by .NET Framework is actually generational. are assigned a generation; newly created objects belong to Generation 0. The objects that survive a garbage collection are tagged as Generation 1, and the Generation 1 objects that survive another collection are Generation 2 objects. The .NET Framework uses up to Generation 2 objects. Higher generation objects are garbage collected less frequently than lower generation objects. This helps increase the efficiency of garbage collection, as older objects tend to have a larger lifetime than newer objects.[Thus, by removing older (and thus more likely to survive a collection) objects from the scope of a collection run, fewer objects need to be checked and compacted.

Different .Net Versions

.NET Framework 1.0

This is the first release of the .NET Framework. Released on February 13, 2002. Available for Windows 98, NT 4.0, 2000, and XP.

.NET Framework 1.1

This is the first major .NET Framework upgrade. It is available on its own as a redistributable package or in a software development kit, and was published on April 3, 2003. It is also part of the second release of Microsoft Visual Studio .NET (released as Visual Studio .NET 2003). This is the first version of the .NET Framework to be included as part of the Windows operating system, shipping with Windows Server 2003.

Changes since 1.0

* Built-in support for mobile ASP.NET controls. Previously available as an add-on for .NET Framework, now part of the framework.
* Security changes - enable Windows Forms assemblies to execute in a semi-trusted manner from the Internet, and enable Code Access Security in ASP.NET applications.
* Built-in support for ODBC and Oracle databases. Previously available as an add-on for .NET Framework 1.0, now part of the framework.
* .NET Compact Framework - a version of the .NET Framework for small devices.
* Internet Protocol version 6 (IPv6) support.
* Numerous API changes.

.NET Framework 2.0

Released with Visual Studio .NET 2005, Microsoft SQL Server 2005, and BizTalk 2006.

* The 2.0 Redistributable Package can be downloaded for free from Microsoft, and was published on 2006-01-22.
* The 2.0 Software Development Kit (SDK) can be downloaded for free from Microsoft.
* It is included as part of Visual Studio 2005 and Microsoft SQL Server 2005.
* Version 2.0 is the last version with support for Windows 2000, Windows 98 and Windows Me.
* It shipped with Windows Server 2003 R2 (not installed by default).

Changes since 1.1

* Numerous API changes.
* A new hosting API for native applications wishing to host an instance of the .NET runtime. The new API gives a fine grain control on the behavior of the runtime with regards to multithreading, memory allocation, assembly loading and more (detailed reference). It was initially developed to efficiently host the runtime in Microsoft SQL Server, which implements its own scheduler and memory manager.
* Full 64-bit support for both the x64 and the IA64 hardware platforms.
* Language support for Generics built directly into the .NET CLR.
* Many additional and improved ASP.NET web controls.
* New data controls with declarative data binding.
* New personalization features for ASP.NET, such as support for themes, skins and webparts.
* .NET Micro Framework - a version of the .NET Framework related to the Smart Personal Objects Technology initiative.

.NET Framework 3.0

.NET Framework 3.0, formerly called WinFX, includes a new set of managed code APIs that are an integral part of Windows Vista and Windows Server 2008 operating systems. It is also available for Windows XP SP2 and Windows Server 2003 as a download. There are no major architectural changes included with this release; .NET Framework 3.0 uses the Common Language Runtime of .NET Framework 2.0. Unlike the previous major .NET releases, there was no .NET Compact Framework release made as a counterpart of this version.

.NET Framework 3.0 consists of four major new components:

* Windows Presentation Foundation (WPF), formerly code-named Avalon; a new user interface subsystem and API based on XML and vector graphics, which uses 3D computer graphics hardware and Direct3D technologies. See WPF SDK for developer articles and documentation on WPF.
* Windows Communication Foundation (WCF), formerly code-named Indigo; a service-oriented messaging system which allows programs to interoperate locally or remotely similar to web services.
* Windows Workflow Foundation (WF) allows for building of task automation and integrated transactions using workflows.
* Windows CardSpace, formerly code-named InfoCard; a software component which securely stores a person's digital identities and provides a unified interface for choosing the identity for a particular transaction, such as logging in to a website.

.NET Framework 3.5

* This version of the framework uses version 2.0 of the CLR (the same model of using CLR 2.0 in .NET Framework 3.0). However, it installs .NET Framework 2.0 SP1, which adds some methods and properties, required for .NET Framework 3.5 features like LINQ, to the BCL classes in .NET Framework 2.0. These changes do not affect applications written for version 2.0 of the .NET Framework.
* Full support for .NET Framework 3.5 project types, and also .NET Framework 3.5 in builds, is included in Visual Studio 2008.
* The source code of the Base Class Library in this release has been released under Microsoft Reference License.
* .NET Framework 3.5 SP1, codenamed "Arrowhead", will enhance support for occasionally connected applications, and provide built-in support for the Microsoft ASP.NET MVC Framework.[16]
* Similar to .NET Framework 1.0 and 2.0, a new .NET Compact Framework 3.5 will be released in tandem with this update, to provide e.g. LINQ, HTTP compression, and improved audio support for mobile devices.
* Officially Released To Manufacturing (RTM) on 19 November 2007.

Changes

* New language features in C# 3.0 and VB.NET 9.0 compiler
* Adds support for expression trees and lambda methods
* Extension methods
* Anonymous types with static type inference
* Language Integrated Query (LINQ) along with its various providers
o LINQ to Objects
o LINQ to XML
o LINQ to SQL
* Paging support for ADO.NET
* ADO.NET synchronization API to synchronize local caches and server side datastores
* Asynchronous network I/O API
* Peer-to-peer networking stack, including a managed PNRP resolver
* Managed wrappers for WMI and Active Directory APIs
* Enhanced WCF and WF runtimes, which let WCF work with POX and JSON data, and also expose WF workflows as WCF services.
* Support for HTTP pipelining and syndication feeds.
* ASP.NET AJAX is included
* New System.CodeDom namespace


.NET vs. Java and Java EE

The CLI and C# have many similarities to Sun's JVM and Java. They are strong competitors. Both are based on a virtual machine model that hides the details of the computer hardware on which their programs run. Both use their own intermediate byte-code, Microsoft calling theirs Common Intermediate Language (CIL; formerly MSIL) and Sun Java bytecode. On .NET, the byte-code is always compiled before execution, either Just In Time (JIT), or in advance of execution using the ngen.exe utility. With Java the byte-code is either interpreted, compiled in advance, or compiled JIT. Both provide extensive class libraries that address many common programming requirements, and both address many security issues that are present in other approaches. The namespaces provided in the .NET Framework closely resemble the platform packages in Java EE API Specification both in style and invocation.

.NET in its complete form (Microsoft's implementation) is currently only fully available on Windows platforms and partially available on Linux and Mac, whereas Java is fully available on nearly all platforms. From its beginning, .NET has supported multiple programming languages, and at its core remains platform agnostic and standardized so that other vendors can reimplement it on other platforms (although Microsoft's implementation only targets Windows, Windows CE, and Xbox based platforms). The Java platform was initially built to support only the Java language, but on many operating system platforms under the slogan, "Write once, run anywhere." Some non-Java other programming languages have been implemented on the Java Virtual Machine, but they are not widely used.

Sun's reference implementation of Java is becoming open source (including the class library, the compiler, the virtual machine, and the various tools associated with the Java Platform) under the copyleft GNU GPL license.

The third-party Mono Project, sponsored by Novell, has been developing an open source implementation of the ECMA standards that define the .NET Framework, as well as most of the other non-ECMA standardized libraries in Microsoft's .NET. The Mono implementation is meant to run on Linux, Solaris, Mac OS, BSD, HP-UX, and Windows platforms. Mono includes the CLR runtime, the class libraries, and compilers for C# and VB.NET. The current version supports nearly all the APIs in version 1.1 of Microsoft's .NET and almost 96% of the APIs in version 2.0 of Microsoft's .NET. Support for the additional libraries in .NET 3.0 and 3.5 is ongoing, and currently in the early alpha stages. Support for C# 3.0 and Linq is also in early alpha at this stage.

Disadvantages

Some concerns and criticisms relating to .NET include:

* Applications running in a managed environment such as the Microsoft framework's CLR or Java's JVM tend to require more system resources than functionally similar applications that access machine resources more directly. However, some applications have been shown to perform better in .NET than in their native version.[citation needed] This could be due to the runtime optimizations made possible by such an environment, the use of relatively well-performing functions in the .NET framework, just-in-time compilation of managed code, or other aspects of the CLR. example, in C++ each time you create a variable the program needs to grab memory from the system - which is a relatively slow operation - so creating lots of variables yields lots of calls to memory. The CLR would optimize this by grabbing larger chunks of memory fewer times and then allocating each variable to parts of that same chunk.
* As JIT languages can be more easily reverse-engineered than native code to algorithms used by an application, there is concern over possible loss of trade secrets and the bypassing of license control mechanisms. However, many obfuscation techniques already developed can help to prevent this; indeed Microsoft's Visual Studio 2005 includes such a tool produced by PreEmptive Solutions.
* In a managed environment such as the Microsoft framework's CLR or Java's JVM, the regularly occurring garbage collection for reclaiming memory suspends execution of the application for an unpredictable lapse of time (typically no more than a few milliseconds). This makes such environments unsuitable for some applications, such as those that must respond to events with sub-second timing.
* Since the framework is not pre-installed on older versions of Windows, an application that requires it must verify that it is present, and if it is not, guide the user to install it. This requirement may deter some from using the application.
* Newer versions of the framework (3.5 and up) are not pre-installed on any versions of the Windows operating system. Some developers have expressed concerns about the size (166 MB) and reliability of .NET framework installers.