How does drupal works?

1. The web server picks the PHP file to run based on the URL That PHP file is (almost) always Drupal core's index.php
2. The PHP file runs. (index.php). It includes a bunch of include files which define helper functions and settings, it connects to the database (which is required) and pulls more settings out of the database, it includes even more files (themes and modules) which define yet more helper functions and callbacks, and finally it decides which function, in all of the combined tens of included files that should be run
3. It calls that function, which is called a "menu callback". This "menu callback" is the first chance that you have to run your own code.
4. Your menu callback runs. It can optionally call PHP standard library functions, include other PHP files for extra functionality, or call any Drupal standard library functions.
5. As the menu callback runs, anything that it outputs is sent to the browser, just like in the raw PHP file case above.
6. But the Drupal Way is for the menu callback to return a string. That string then gets plugged into a template page for the site (which is one component of a theme), and the template page with the string plugged into the right spot gets sent back to the browser.

Advantages & disadvantages of drupal

Advantages of the Drupal way of doing things:

1. It's consistent. For example, if you always use the "correct" way to print out usernames, changing the style of those printed usernames in one place changes them across the entire site.
2. It's integrated.
3. It's convenient.

But there are some disadvantages:

1. It's slow(er).
2. It uses memory.

Whats new in Drupal 7?

1.Better user interface for administrator & users
2.Dashboard menu for administrator to display some important content on login of administrator. it is more often configurable.
3.IP Address blocking configuration is provided.
4.CCK,imagecache & URL alias is in built in Drupal.
5.Naming convention are changed in drupal for eg.Themes are represented as Appearance & User links are represented as people.
6.Module list page itself contains the link to its permission & Configuration.
7.Upload module in user interface itself .Module list page has provision to upload an module folder in an specified format.
8.All files in the module other than module file must be declared in the info file of that module.
9.If the module uses any admin configuration then the configuration path must be declared in the info file