"I had Windows computers back in the day, late 90s, where I only upgraded the hardware, not the OS." How would that be possible since Windows almost invariably

"I had Windows computers back in the day, late 90s, where I only upgraded the hardware, not the OS." How would that be possible since Windows almost invariably came pre-installed by OEMs. New hardware would have the latest Windows version pre-installed. Downgrading would be extremely difficult if not impossible.