What is the difference between HTML, PHP, ASP or C#?

The main difference is that HTML is a tag language, which is used to describe the public part of the site. The language is quite simple and was firstly developed to present text information in the browser. Browsers till this day can only show HTML part of the site.

Using HTML it is impossible to manage site content. User would have to work with a server directly using FTP-protocol to upload the pictures, download the pages and update the text in them at his own risk.

In case the site is fully programmed in HTML and CSS (styles file with the help of which a uniform appearance for all the pages is provided), it is necessary to possess programming knowledge, otherwise site owner will have to pay to the developers to update any information, which, as you understand, leads to great costs since most of the present web sites are very dynamic, being a marketing tool rather than just a picture.

So, we know that in order to get a dynamic site we need something else besides HTML and CSS. How can we determine what language to use further: PHP, ASP or #C?

PHP, ASP, C# — are script languages of a higher level, which allow to create scripts that address user requests to the data base (DB). As a result of the script work, user receives some information. For example, during site search, user makes an entry into the field, clicks "enter" (which starts the work of the script), then receives a list of links that was made by the script.

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In the picture: work of a web site:  PHP-scripts process the data which are kept on the server. The processed data are reflected to users and site administrator as HTML-templates. 

Any work with DB means usually that there's either PHP or ASP, C# involved.

Before choosing the development language you, as a customer, need to take following into account:

1) Cost of hosting.
Usually, Windows-hosting costs more and this is connected to the cost of DB MsSQL 2000.

2) Cost of developer services.
This factor depends on market circumstances: as of today, C#-developer services are more expensive than PHP-developer services. We believe that these are the main factors which can be determined without describing the task to be solved.

In a number of cases the task itself already contains the only right choice: PHP, ASP, C#.