Windows 32-bit or 64-bit: which to install, and does one key fit both?

Nearly every PC from the last 15 years should run 64-bit.

The difference

32-bit Windows sees only about 4 GB of RAM. 64-bit uses all of it and runs modern software. Windows 11 exists only in 64-bit.

How to check yours

Settings, System, About, System type.

Does one key fit both?

Yes. The key is for the edition, not for the bitness.

Moving from 32 to 64-bit

It needs a clean install from USB. Your licence stays valid.

Office bitness

Choose 64-bit unless an old add-in needs 32-bit.