Chromium is an operating system that only has a web browser interface. Chromium is an open-source project that provides the source code and framework for Chrome OS, which is a Linux-based operating system developed by Google. Chromium and Chrome OS are designed to run web applications and cloud services through the Chrome web browser, which is the only user interface available on the system. Chromium and Chrome OS are mainly used on devices such as Chromebooks, Chromeboxes and Chromebits. Linux is an operating system that does not only have a web browser interface but also a graphical user interface and a command-line interface. Linux is an open-source and customizable operating system that can run various applications and services on different devices and platforms. Linux can also support different web browsers, such as Firefox, Opera and Chromium. Microsoft Windows is an operating system that does not only have a web browser interface but also a graphical user interface and a command-line interface. Microsoft Windows is a proprietary and popular operating system that can run various applications and services on different devices and platforms. Microsoft Windows can also support different web browsers, such as Edge, Internet Explorer and Chrome. iOS is an operating system that does not only have a web browser interface but also a graphical user interface and a voice-based interface. iOS is a proprietary and mobile operating system developed by Apple that can run various applications and services on devices such as iPhone, iPad and iPod Touch. iOS can also support different web browsers, such as Safari, Firefox and Chrome. References: CompTIA A+ Core 2 (220-1002) Certification Exam Objectives Version 4.0, Domain 1.1