Which step should be taken before starting the OS installation?

Backing up any old data is a crucial step before starting an operating system installation. This process is essential for safeguarding important information that may be lost during the installation. Operating system installations can sometimes lead to data loss, particularly if you are formatting the disk or if unexpected errors occur during the installation process. By backing up existing data, users ensure that any valuable files, documents, or personal information are preserved and can be restored later if needed.

Other options, while potentially relevant to the overall maintenance or preparation of a system, do not address the immediate need to protect data. Running updates is good practice but does not prevent data loss during installation. Installing new applications is generally more suitable post-installation, as the new OS may require fresh installations of compatible versions. Disconnecting peripherals might help streamline the installation process, but it does not mitigate the risk of data loss. Thus, prioritizing data backup serves as a necessary precaution for a smooth transition to a new operating system.