Windows 95 almost had floppy insertion detection

One of the Windows developers reveals at The Old New Thing blog that Windows 95 almost had the ability to detect when a floppy disk was present in the drive without spinning up the drive. This feature was technically possible, but it was abandoned because there are two different floppy hardware specification implementations that produce exactly opposite results. There was an idea to make the user go through a training so the operating system could detect the style of the floppy drive, but this wasn't really practical.

The person responsible for Windows 95's 32-bit floppy driver studied the floppy drive hardware specification and spotted an opportunity. Working through the details of the specification revealed that, yes, if you issued just the right extremely clever sequence of commands, you could determine whether a disk was in the floppy drive without spinning up the drive. But there was a catch.

The floppy drive hardware specification left one aspect of the drive behavior unspecified, and studying the schematics for various floppy drive units revealed that about half of the floppy drive vendors chose to implement it one way, and half the other way.

The results were completely reliable within each "style" of floppy drive, but the two styles produce exactly opposite results. If you knew which style of drive you had, then the results were meaningful, but the hard part was deciding which style of drive the user had.