files, not ISOs. If you need an ISO for a virtual machine or specific boot tool, it is safer to convert the official installer yourself rather than downloading a pre-made ISO from a forum. OS X El Capitan - Technical Specifications - Apple Support
Ensuring the downloaded ISO is of high quality and secure involves several steps: download iso mac os x el capitan high quality
Disclaimer: This guide is for educational purposes and for users who legitimately own Apple hardware capable of running El Capitan. files, not ISOs
Mac App Store (if you have access to an older Mac running a compatible macOS): download iso mac os x el capitan high quality