If you have a legacy Visual Studio subscription (formerly MSDN), you can download the original 1507 ISOs from the "My Downloads" section. These are the definition of "extra quality"—official, signed, and untouched.
Some retro PC builders prefer 1507 because it has better compatibility with late-2000s DX9 games than Windows 11, yet it supports modern SSDs and RAM. It is the "Goldilocks" zone for a Core 2 Duo or first-gen i7 build.
Do not use Windows 10 1507 as your primary, internet-connected operating system. windows 10 pro 1507 iso download extra quality
Because support ended in May 2017, this build is missing critical security patches for vulnerabilities like:
If you install 1507, keep it offline. Use it for virtual machines, legacy labs, or archival purposes only. If you have a legacy Visual Studio subscription
If you manage to download an ISO, do not install it until you verify it hasn't been tampered with. This is how you ensure "extra quality."
Here are the official SHA1 hashes for the English (United States) Windows 10 Pro RTM (Build 10240) ISO: If you install 1507, keep it offline
In 1507, this is much easier than Windows 11. During OOBE (Out of Box Experience), simply unplug the Ethernet cable. Click "Skip" or "Create a local account." Microsoft did not force online accounts in this build.