The .NET Framework 4 Client Profile supports more platforms than in previous versions and provides a fast deployment experience for your Windows Presentation Foundation (WPF), console, or Windows Forms applications. For more information, see .NET Framework Client Profile.

This feature enables an application to load and start multiple versions of the .NET Framework in the same process. For example, you can run applications that load add-ins (or components) that are based on the .NET Framework 2.0 SP1 and add-ins that are based on the .NET Framework 4 in the same process. Older components continue to use the older .NET Framework version, and new components use the new .NET Framework version. For more information, see In-Process Side-by-Side Execution.

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Earlier versions of the .NET Framework provided no way to determine whether a particular application domain was affecting other application domains, because the operating system APIs and tools, such as the Windows Task Manager, were precise only to the process level. Starting with the .NET Framework 4, you can get processor usage and memory usage estimates per application domain.

You can monitor CPU and memory usage of individual application domains. Application domain resource monitoring is available through the managed and native hosting APIs and event tracing for Windows (ETW). When this feature has been enabled, it collects statistics on all application domains in the process for the life of the process. See the new AppDomain..::.MonitoringIsEnabled property.

You can now access the ETW events for diagnostic purposes to improve performance. For more information, see CLR ETW Events and Controlling .NET Framework Logging. Also see Performance Counters and In-Process Side-By-Side Applications.

The System.Runtime.ExceptionServices..::.HandleProcessCorruptedStateExceptionsAttribute attribute enables managed code to handle exceptions that indicate corrupted process state.

The .NET Framework 4 provides background garbage collection. This feature replaces concurrent garbage collection in previous versions and provides better performance. For more information, see Fundamentals of Garbage Collection.

Code contracts let you specify contractual information that is not represented by a method's or type's signature alone. The new System.Diagnostics.Contracts namespace contains classes that provide a language-neutral way to express coding assumptions in the form of preconditions, postconditions, and object invariants. The contracts improve testing with run-time checking, enable static contract verification, and support documentation generation. For more information, see Code Contracts.

You no longer have to ship primary interop assemblies (PIAs) to deploy applications that interoperate with COM objects. In the .NET Framework 4, compilers can embed type information from interop assemblies, selecting only the types that an application (for example, an add-in) actually uses. Type safety is ensured by the common language runtime. See Using COM Types in Managed Code and Walkthrough: Embedding Type Information from Microsoft Office Assemblies (C# and Visual Basic).

The dynamic language runtime (DLR) is a new runtime environment that adds a set of services for dynamic languages to the CLR. The DLR makes it easier to develop dynamic languages to run on the .NET Framework and to add dynamic features to statically typed languages. To support the DLR, the new System.Dynamic namespace is added to the .NET Framework.

The expression trees are extended with new types that represent control flow, for example, System.Linq.Expressions..::.LoopExpression and System.Linq.Expressions..::.TryExpression. These new types are used by the dynamic language runtime (DLR) and not used by LINQ.

In addition, several new classes that support the .NET Framework infrastructure are added to the System.Runtime.CompilerServices namespace. For more information, see Dynamic Language Runtime Overview.

Several generic interfaces and delegates now support covariance and contravariance. For more information, see Covariance and Contravariance in Generics.

The new System.Numerics..::.BigInteger structure is an arbitrary-precision integer data type that supports all the standard integer operations, including bit manipulation. It can be used from any .NET Framework language. In addition, some of the new .NET Framework languages (such as F# and IronPython) have built-in support for this structure.

The new System.Numerics..::.Complex structure represents a complex number that supports arithmetic and trigonometric operations with complex numbers.

The .NET Framework 4 provides the System..::.Tuple class for creating tuple objects that contain structured data. It also provides generic tuple classes to support tuples that have from one to eight components (that is, singletons through octuples). To support tuple objects that have nine or more components, there is a generic tuple class with seven type parameters and an eighth parameter of any tuple type. 

New file enumeration methods improve the performance of applications that access large file directories or that iterate through the lines in large files. For more information, see How to: Enumerate Directories and Files.

The .NET Framework now supports memory-mapped files. You can use memory-mapped files to edit very large files and to create shared memory for interprocess communication.

You can identify 64-bit operating systems and processes with the Environment..::.Is64BitOperatingSystem and Environment..::.Is64BitProcess properties.

You can specify a 32-bit or 64-bit view of the registry with the Microsoft.Win32..::.RegistryView enumeration when you open base keys.

The following list describes additional new capabilities, improvements, and conveniences. Several of these are based on customer suggestions.

• To support culture-sensitive formatting, the System..::.TimeSpan structure includes new overloads of the ToString, Parse, and TryParse methods, as well as new ParseExact and TryParseExact methods.

• The new String..::.IsNullOrWhiteSpace method indicates whether a string is null, empty, or consists only of white-space characters. New overloads have been added to the String.Concat and String.Join methods that concatenate members of System.Collections.Generic..::.IEnumerable<(Of <(T>)>) collections.

• The String..::.Concat method lets you concatenate each element in an enumerable collection without first converting the elements to strings.

• Two new convenience methods are available: StringBuilder..::.Clear and Stopwatch..::.Restart.

• The new Enum..::.HasFlag method determines whether one or more bit fields or flags are set in an enumeration value. The Enum..::.TryParse method returns a Boolean value that indicates whether a string or integer value could be successfully parsed.

• The System..::.Environment..::.SpecialFolder enumeration contains several new folders.

• You can now easily copy one stream into another with the CopyTo method in classes that inherit from the System.IO..::.Stream class.

• New Path..::.Combine method overloads enable you to combine file paths.

• The new System..::.IObservable<(Of <(T>)>) and System..::.IObserver<(Of <(T>)>) interfaces provide a generalized mechanism for push-based notifications.

• The System..::.IntPtr and System..::.UIntPtr classes now include support for the addition and subtraction operators.

• You can now enable lazy initialization for any custom type by wrapping the type inside a System..::.Lazy<(Of <(T>)>) class.

• The new System.Collections.Generic..::.SortedSet<(Of <(T>)>) class provides a self-balancing tree that maintains data in sorted order after insertions, deletions, and searches. This class implements the new System.Collections.Generic..::.ISet<(Of <(T>)>) interface.

• The compression algorithms for the System.IO.Compression..::.DeflateStream and System.IO.Compression..::.GZipStream classes have improved so that data that is already compressed is no longer inflated. Also, the 4-gigabyte size restriction for compressing streams has been removed.

• The new Monitor..::.Enter(Object, Boolean%) method overload takes a Boolean reference and atomically sets it to true only if the monitor is successfully entered.

• You can use the Thread..::.Yield method to have the calling thread yield execution to another thread that is ready to run on the current processor.

• The System..::.Guid structure now contains the TryParse and TryParseExact methods.

• The new Microsoft.Win32..::.RegistryOptions enumeration lets you specify a volatile registry key that does not persist after the computer restarts.

• Registry keys are no longer restricted to a maximum length of 255 characters.

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In the .NET Framework 4, Windows Presentation Foundation (WPF) contains changes and improvements in many areas, including controls, graphics, and XAML. For more information, see What's New in WPF Version 4.

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ADO.NET provides new features for the Entity Framework, including Persistence-Ignorant Objects, functions in LINQ queries, and Customized Object Layer Code Generation. For more information, see What's New in ADO.NET.

For ASP.NET 4, Dynamic Data has been enhanced to give you even more power for quickly building data-driven Web sites. This includes the following:

• Automatic validation that is based on constraints that are defined in the data model.

• The ability to easily change the markup that is generated for fields in the GridView and DetailsView controls by using field templates that are part of a Dynamic Data project.

For more information, see What's New in ASP.NET 4 and Visual Web Developer.

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