Windows 3.1 was distributed on a series of 3.5-inch or 5.25-inch floppy disks (typically 6 to 7 high-density disks). ISO files are sector-by-sector copies of optical discs (CDs/DVDs). Because CD-ROM drives were rare luxuries in 1992, Microsoft did not sell Windows 3.1 on CDs. Therefore, any "Windows 3.1 ISO" you find online is a modern, fan-made compilation. 2. Where to Download Windows 3.1 Files Safely
The premier digital museum for abandonware. They host original, unmodified floppy disk images (usually in .IMG or .IMA format) for Windows 3.1, Windows 3.11 for Workgroups, and various versions of MS-DOS. windows 3.1 bootable iso download