Managed Code is code that is written to target the services of the
managed runtime execution environment (CLR). The Managed Code is always
executed by managed Code runtime environment rather than OS directly. It
refers to a method of exchanging information between the program and
the runtime enviornment. The environment also provide the necessary
security checks before executing piece of code. Managed code also get
different services from the untime environment like
Garbage collection
Type Safety
Exception handling.
Bounds Checking
Therefore managed code does not have to worry about memory
allocations, type safety. Applications written in java, c#, VB.net, etc
target a runtime environment which manages the execution and the code
written using these languages is known as managed code. Managed Code is
always compiled into a intermediate languages (MSIL in Dot net).
These compiler used by .net framework to compile managed code
compiles it into an intermediate language and generate necessary
metadata and information.
In .Net framework managed code runs with in the .net framework’s CLR
and get all services provided by CLR. After compile managed code an
executable is created. When user run the executable the Just in time
compiler of CLR compiles IL into native code specific to architecture of
machine or machine code.
Managed Code also provides platform independence. As the managed
code is first compiled to IL, the CLR’s JIT compiler takes care of
compiling this IL into architecture specific instructions.
Unmanaged Code
Code that is directly executed by the operating System is known as
an un-managed code. Applications written in VB 6.0, C++, C etc are all
examples of unmanaged code. Unmanaged code typically targets the
processors architecture and is always dependent on the computer
architecture. If you want to run the same code on different architecture
then you have to recompile the code using that particular architecture.
Unmanaged code is always compiled to the native code. Unmanaged code
does not get any services from the managed execution environment.
In unmanaged code the memory allocation, type safety, security needs
to be taken care of by the developer. This makes unmanaged code prone
to memory leaks like buffer over burns and pointer overrides etc.
Difference between Managed Code and Unmanaged Code
Code that targets the common language runtime is known as managed
code. But unmanaged code is executed directly by operating System.
Managed Code is executed under the instruction of CLR. But unmanaged cannot executed under the instruction of CLR.
The code is understandable by CLR in case of managed. But in case of unmanaged code is not understand by CLR.
In managed code compilation process is done is two phase- Code to
MSIL and then MSIL to machine language. But in case of unmanaged code,
the code compilation is done in one phase, code to machine code.
Languages used in writing managed code are, Java, C#, VB.net, etc
which uses runtime environment. But languages used in writing unmanaged
code are vb 6.0, C++, C etc.
Managed code provides Garbage Collection or Automatic memory
allocation and de-allocation. But unmanaged code does not provide memory
allocation features.
Managed code also provides platform independence. But unmanaged code is platform dependence.
In case of managed code is compiled into MSIL (Microsoft
intermediate Language). In case of unmanaged code, code is compiled into
machine language.
Managed Code provides Type Safety. But unmanaged does not provide Type Safety.
Unmanaged code is more error prone then managed code.
In unmanaged code the memory allocation or other services needs to
be taken care of by the developer. But developer is no need to take care
of these services in managed code.
Key Features available to managed code applications includes.
Performance gained from executing all code in the CLR. Calling
unmanaged code decrease performances because addition security check are
required.
Ease of deployment and vast improved versioning facilities the end of “DLL Hell”.
Built-in Security by using code access security and avoiding buffer overruns.
It provides scalability features.
Provide improvement to application stability.
Provide cross-language integration.
This permits applications built with managed code to perform more safety and efficiently.