The operating system is at such a low level in the stack that Drupal does not care much about it. Drupal runs successfully on any operating system that supports PHP.

Because of Drupal’s long history with Apache, Drupal ships with .htaccess files that secure the Drupal installation. Clean URLs—that is, those devoid of question marks, ampersands, or other strange characters—are achieved using Apache’s mod_rewrite component.
Extra:
Drupal interfaces with the next layer of the stack (the database) through a lightweight database abstraction layer, which was totally rewritten in Drupal 7. The database interface provides an API based on PHP data object (or PDO) and allows Drupal to support any database that supports PHP. The most popular databases include MySQL and PostgreSQL. In Drupal 7, SQLite is now also supported.