Windows 95 was too fat to install itself so slim 3.1 helped
Microsoft used a miniature Windows 3.1 during Windows 95 setup because it was smaller, required fewer reboots, and already existed, saving time and engineering effort.
Microsoft removed the HLT instruction from Windows 95 because numerous devices would lock up and the company couldn't reliably detect all affected systems.
Windows 95 testing almost stalled from cash reg overflow
Windows 95's compatibility testing involved a unique initiative where engineers tested numerous applications, leading to an unexpected cash register overflow incident during software acquisition.