Difference between ASP.NET and ASP
Dear friends here is a list of differences of the ASP.NET technology and the classic ASP technology.Hope it is informative. Please send your feedback or/and add if you have additional information.

Introduction

These are the list of differences which I came across while working on ASPand ASP.NET projects.

Background

I have seen many articles on Internet where in I came across the differences of ASP.NET and ASP. These articles are jumbled across the websites. I have compiled all those and published this article to give better understanding on the differences of both.

Description

ASP is run under the inetinfo.exe(IIS) process space and hence susceptible to application crashes as a result the IIS needs to be stopped or restarted. ASP is related to the process isolation setting in IIS. But, ASP.Net
The ASP.NET worker process is a distinct worker process, aspnet_wp.exe, separate from inetinfo.exe ( IIS process), and the process model in ASP.NET is unrelated to process isolation settings in IIS.

Classical ASP had no mechanism of running itself on non- Microsoft technology platforms like the 'The Apache Web Server'
But, ASP.NET
ASP.NET could be run on non-Microsoft Platforms also. Cassini is a sample Web server produced by Microsoft which, among other projects, has been used to host ASP.NET with Apache.



In ASP only two languages were available for scripting VBScript and Jscript/Javascript. But in ASP.NET We are no longer constrained to the two scripting languages available in traditional ASP: Any fully compliant .NET language can now be used with ASP.NET, including C# and VB.NET.



In ASP, ASP engine executes server-side code, which is always through an interpreter (JScript or VBScript). When a traditional ASP page is requested, the text of that page is parsed linearly. All content that is not server-side script is rendered as is back to the response. All server-side script in the page is first run through the appropriate interpreter (JScript or VBScript), the output of which is then rendered back to the response. This architecture affects the efficiency of page rendering in several ways. First, interpreting the server-side script on the fly.As a side effect, one common optimization for ASP applications is to
move a lot of server-side script into precompiled COM components to improve response times. A second efficiency concern is that intermingling server-side evaluation blocks with static HTML is less efficient than evaluating a single server-side script block, because the interpreter has to be invoked over and over again. Thus, to improve efficiency of rendering, many ASP developers resort to large blocks of server-side script, replacing static HTML elements with Response.Write() invocations instead. Finally, this ASP model actually allows different blocks of script within a page to be written in different script languages. While this may be appealing in some ways, it also degrades performance by requiring that a particular page load both scripting engines to
process a request, which takes more time and memory than using just one language. But in ASP.NET, In contrast, ASP.NET pages are always compiled into .NET classes housed within assemblies. This class includes all of the server-side code and the static HTML, so once a page is accessed for the first time (or any page within a particular directory is accessed), subsequent rendering of that page is serviced by executing compiled code. This eliminates all the inefficiencies of the scripting model of traditional ASP. There is no longer any performance difference between compiled components and server-side code embedded within a page they are now both compiled components. There is also no performance difference between interspersing server-side code blocks among static HTML elements, and writing large blocks of server-side code and using
Response.Write() for static HTML content. Also, because the .aspx file is parsed into a single code file and compiled, it is not possible to use multiple server-side languages within a single .aspx file.
In classic ASP it was very difficult for us to debug the application. ASP developers had time to debug application due to limited support due to the interpreted model.
But in ASP.NET In addition to improved performance over the interpreted model, pages that are compiled into classes can be debugged using the same debugging tools available to desktop applications or component developers. Errors with pages are generated as compiler errors, and there is a good chance that most errors will be found at compilation time instead of runtime, because VB.NET and C# are both strongly typed languages. Plus, all the tools available to the .NET developer are applicable to the .aspx developer.
class=docText>Especially if you are using ASP pages it is possible to include executable code outside the scope of a function within a script block marked as runat=server, and , it is possible to define a function within a pair of server-side script tags.
But in ASP.NET, In ASP.NET it is no longer possible to include executable code outside the scope of a function within a script block marked as runat=server, and conversely, it is no longer possible to define a function within a pair of server-side script tags.

Note also that the generated class definition provides a default constructor for you, and if you try to define your own default constructor within your page, it will cause a compiler error. This can be somewhat frustrating if you are trying to properly initialize elements of your class (such as filling up our array of values or subscribing to events). Fortunately, an alternative technique gives you more complete control over the class definition while separating the layout from the page logic. This technique is called code-behind.

In traditional ASP applications, components used by pages and deployed in this fashion were notoriously difficult to update or replace. Whenever the application was up and running, it held a reference to the component file so to replace that file, you had to shut down IIS (temporarily taking your Web server offline), replace the file, and restart IIS.
But in ASP.NET, The goals of ASP.NET was to eliminate the need to stop the running Web application whenever components of that application need to be updated or replaced that is, updating an application should be as simple as using xcopy to replace the components on the Web server with the new updated versions. To achieve this xcopy deployment capability, the designers of ASP.NET had to ensure two things: first, that the running application not hold a reference to the component file and second, that whenever the component file was replaced with a new version, that new version was picked up with any subsequent requests made to the application. Both of these goals are achieved by using the shadow copy mechanism provided by the Common Language Runtime (CLR).
Shadow copying of assemblies is something you can configure when you create a new application domain in .NET. The AppDomainSetup class (used to initialize an AppDomain) exposes a Boolean property called ShadowCopyFiles and a string property called CachePath, and the AppDomain class exposes a method called SetShadowCopyPath() to enable shadow copying for a particular application domain. The Boolean property turns the mechanism on for a particular application domain, the CachePath specifies the base directory where the shadowed copies should be placed, and the SetShadowCopyPath() method specifies which directories should have shadow copying enabled.
ASP.NET creates a distinct application domain for each application it hosts in its worker process and for each application domain, it enables shadow copying of all assemblies referenced in the /bin directory. Instead of loading assemblies directly from the /bin directory, the assembly loader physically copies the referenced assembly to a separate directory (also indicated in the configuration settings for that application domain) and loads it from there. This mechanism also keeps track of where the assembly came from, so if a new version of that assembly is ever placed in the original /bin directory, it will be recopied into the Noteshadow" directory and newly referenced from there.
In addition to shadow copying of assemblies, ASP.NET needs the ability to create and load assemblies on the fly. The first time an .aspx page is referenced, as we have seen, it is compiled into an assembly and loaded by ASP.NET. What we haven't seen is where those assemblies are located once they are compiled. Application domains also support the concept of a "dynamic directory" specified through the DynamicBase property of the AppDomainSetup class, which is a directory designed for dynamically generated assemblies that can then be referenced by the assembly loader. ASP.NET sets the dynamic directory of each application it houses to a subdirectory under the system Temporary ASP.NET Files directory with the name of the virtual directory of that application.
One consequence of both dynamic assembly generation and shadow copying is that many assemblies are copied during the lifetime of an ASP.NET application. The assemblies that are no longer being referenced should be cleaned up so that disk space usage doesn't become a limiting factor in application growth. In ASP.NET shadow copied assemblies are removed as soon as possible after a new version of that assembly is copied, and dynamically generated assemblies that are no longer used are cleaned up the next time the ASP.NET worker process is bounced and the particular application associated with the dynamic assemblies is run again. In general, this means that you shouldn't have to worry about unused assemblies generated by ASP.NET wasting space on your machine for very long.



The threading model of COM object created using VB within a web-based application is STA. ASP worker thread resides in its own STA and hence the compatability is fine in this case with a little performance hit.
But in ASP.NET, The ASP.NET threading model is the Multiple Threaded Apartment (MTA). What this means is that components that you are using that were created for the Single Threaded Apartment (STA) will no longer perform or function reliably without taking some extra precautions in ASP.NET. This includes, but is not limited to, all COM components that have been created using Visual Basic 6.0 and earlier versions. You will be glad to hear that you can still use these STA components without having to change any code. What you need to do is include the compatibility attribute aspcompat=true in a <%@Page> tag on the ASP.NET page. For example, <%@Page aspcompat=true Language=VB%>. Using this attribute will force your page to execute in STA mode, thus ensuring your component will continue to function correctly. If you attempt to use an STA component without specifying this tag, the run time will throw an exception. Setting this attribute to true will also allow your page to call COM+ 1.0 components that require access to the unmanaged ASP built-in objects. These are accessible via the ObjectContext object. If you set this tag to true, your performance will degrade slightly. I suggest doing this only if you absolutely need to.

• ASP has no inbuilt facility for Validation of controls.i.e, checking whether a textbox is left blank or not or a combo is selected or not or if a phone number does not fit a particular pattern for a area and many such examples.

• The user had to write the client side Javascript code for all these kind of validations.

• Client and server side validation both were the headache of the of the developer.

• Javascript code to fit a particular Browser was also the developer's burden. He had to write specific code so that it could fit a set of browsers. It took lot of the developers time.

But in ASP.NET, In built validation controls are provided which are as easy to implement and the developer has to worry the least.
The features provided by ASP.NET validation controls is :-

• Browser Independent coding :- Developer does not have to worry about the browser how the controls would render to.

• Client-Side or Server-Side :- The Validation Controls manage the code checking if the client side code is disabled the validation is done on the server side.

Rich Validation set :- There are 6 types of validation which cater to the needs of the validation requirements:

• RequiredFieldValidation Control - Requires that the control not be left blank.

• CompareValidator Control - Used to compare Data in Two Controls

• RangeValidator Control - Used to check for Range validation.(also supports various data Type - Date , string etc..)

• RegularExpressionValidator Control - Used to check the complicated patterns in the user input.

• CustomValidator Control- The final control we have included in ASP.NET is one that adds great flexibility to our validation abilities. We have a custom validator where we get to write out own functions and pass the control value to this function.

This control also provides Client side and server side validation of which the Server side validation could be a different function altogether.

• Validation Summary - The validation summary control will collect all the error messages of all the non-valid controls and put them in a tidy list. The list can be either shown on the web page (as shown in the example above) or with a popup box

Conclusion

This article targets to the developers who have directly started working on ASP.Net and also for the web developers who have migrated from ASP to ASP.Net. This article is at the draft level and might need additions which I intend to do.I welcome suggestion or criticism!! I would request to add as much feedback to this article post as possible. I would keep this post updated.

References

• A very indepth look at the differences. - Excellent.

• (W3Schools - Good article)

• A Comprehensive Description of the Difference- Worth Reading

• A brief difference - Very Good