Note: this page should not be edited without first discussing the changes in a Drupal Core issue as the requirements for each version of Drupal are decided upon by the Drupal Core developers.
A minimum installation requires 15 Megabytes. 60 MB is needed for a website with many contributed modules and themes installed. Keep in mind you need much more for the database, files uploaded by the users, media, backups and other files.
Apache, Nginx, or Microsoft IIS
More details about web server requirements.
Drupal 6: MySQL 4.1 or higher, PostgreSQL 7.1,
Drupal 7: MySQL 5.0.15 or higher with PDO, PostgreSQL 8.3 or higher with PDO, SQLite 3.3.7 or higher
Microsoft SQL Server and Oracle are supported by additional modules.
More details about database requirements.
Drupal 6: PHP 4.4.0 or higher (5.2 recommended).
Drupal 7: PHP 5.2.5 or higher (5.3 recommended).
Drupal 8: PHP 5.3.10 or higher.
More details about PHP requirements.