Electronic Software Distribution format — a high-compression file used by Windows 8.1 and later, but not natively used by Microsoft for Windows 7. This means someone converted the official WIM (Windows Imaging Format) into ESD to shrink the ISO size.
: Windows 7 no longer receives security updates from Microsoft. Using it online poses a significant security risk. win7-ult-sp1-x64-u-24535-esd.iso