Common Language
Runtime
The Common Language Runtime
(CLR) is a layer between an application and theoperating system it executes on.
The CLR simplifies an application's design and reducesthe amount of code
developers need to write because it provides a variety of executionservices
that include memory management, thread management, component
lifetimemanagement, and default error handling. The key benefit of the CLR is
that ittransparently provides these execution services to all applications,
regardless of whatprogramming language they're written in and without any
additional effort on the part ofthe developer.
The CLR is also responsible
for compiling code just before it executes. Instead ofproducing a binary
representation of your code, as traditional compilers do, .NETcompilers produce
a representation of your code in a language common to the .NETFramework:
Microsoft Intermediate Language (MSIL), often referred to as IL. When yourcode
executes for the first time, the CLR invokes a special compiler called a Just
In Time(JIT) compiler, which transforms the IL into executable instructions
that are specific tothe type and model of your system's processor. Because all
.NET languages have thesame compiled representation, they all have similar
performance characteristics. Thismeans that a program written in Visual Basic
.NET can perform as well as the sameprogram written in Visual C++ .NET.
Common
Type System
The Common Type System
(CTS) is a component of the CLR and provides a common set of data types, each
having a common set of behaviors. In Visual Basic, for example, the String data
type maps to the CTS System.String class. Therefore, if a Jscript .NET client
needs to communicate with a component implemented in VB .NET, the client
doesn't have to do any additional work to exchange information because it's
using a type common to both JScript .NET and VB .NET. The CTS eliminates
many interoperability problems that exist outside .NET.
.NET programming languages take
advantage of the CTS by enabling developers to use their language's built-in
data types — the .NET compilers convert the native data types' into their
equivalent CTS types at compile time. Developers can also use CTS types
directly in their code.
.NET Class
Library
In an earlier section,
"Consistent programming models across programming languages,"the .NET
Class Library was described as containing hundreds of classes that model thesystem
and services it provides. To make the .NET Class Library easier to work with
andunderstand, it's divided into namespaces. The root namespace of the .NET
Class Libraryis called System, and it contains core classes and data types,
such as Int32, Object,Array, and Console. Secondary namespaces reside within
the System namespace.
Unifying components
Until this point, this
covered the low-level components of the .NETFramework. The unifying
components, listed next, are the means by which you canaccess the services
the .NET Framework provides:-
§ ASP.NET
§ Windows Forms
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