There are few main technical aspects what powers Drupal technology. Most of them are commonly used by popular CMSs, but in Drupal they are on higher level. 

Drupal technology is empowered:

• backend is PHP as main programming language;
• full OOP by PHP;
• frontend based on HTML, CSS, JavaScript and Twig;
• advanced cache system;
• high-performance server(s) and web server;
• various Operating Systems;
• various Databases;
• parts of Symfony framework;

PHP

Personal Home Page or Hypertext Preprocessor is a programming language which is oriented for making dynamic webpages. PHP is the backend language. In year 2020, 8 version of PHP announcement. Less than 80% of all websites are made in PHP Usage Statistics and Market Share of PHP for Websites, January 2021 (w3techs.com). Also, there are some experience of integrating Python and Node.js in Drupal.

OOP

Object-Oriented Programming is a special way of programming by dividing software into objects. By this, web developers who make later changes can more easily access to different parts of application. This way of programming is more advanced, secured, but it takes more resources. Starting with Drupal 8 that CMS is fully constructed in PHP but in OOP.

HTML, CSS and JavaScript

HTML is the basic building cell of all websites. It is markup language. CSS makes websites more beautiful and much more. It is styling language. JavaScript or JS is a real programming language that makes design dynamic. It is also called script language. All of them are indictable part of all websites, so it is same case with Drupal.

Twig

Twig is specifically template engine based on HTML and PHP. It is made by Symfony developers which purpose is to help developers make secure and high speed design. Instead of pure HTML, working in Twig is more flexible and secure. Twig is something between markup and programming language. It powers the frontend with sanitized HTML, which is more secure. Twig is big advance from Drupal 7.

Caching

A cache is storage for temporary copies of often used parts of a webpage. Instead of repeated loading entire webpage for the visitor, cached pages are displayed instantly. That significantly reduce time of loading page. Drupal cache is raised to a whole new level and improves performance much better than other CMSs.

Server and web server

Drupal is suitable for work on every type of hardware servers. But recommendation is high-performance server(s) because of complex Drupal architecture. So, hosting can be scaled from cheap shared to highly dedicated servers. Also, most common web server software programs like Litespeed, Apache and Nginx is part of Drupal technology. Nginx is recommended because of its performance.

OS

Operating systems that support Drupal are numerous Unix, Linux, BSD, OS X and Windows.

Databases

Drupal supports MySQL (like MariaDB), PostgreSQL and SQLite. Also, it can support Microsoft SQL server and Oracle Database. But for best performance, MariaDB is recommended.

Symfony

High security open-source framework based on PHP. It is suitable for making large, complex and high-performance web application. Symfony is well known because of its modularity, what means that developers can use just components they need instead of all frameworks. Drupal uses many of Symfony components.