An OA (Original Equipment Manufacturer) ISO is a type of Windows installation media that is specifically designed for OEM (Original Equipment Manufacturer) partners. It's used to create a recovery or installation disk for a specific computer.
Microsoft no longer hosts official Windows 7 download links on its main site. Since you have an OEM license, the standard Microsoft download tool often rejects these keys, directing you to the manufacturer instead. windows 7 home premium oa iso download