The size, capacity and type of Microsoft’s Windows installation media has changed dramatically over the years. Longevity of each type of media has also changed.
Windows 1.0 Distributed on 5¼ floppy disks, single sided 160 Kbytes (KiloBytes)
Windows 1.1 Distributed on 5¼ floppy disks, double sided 320 Kbytes (Kilobytes)
Windows 2.x Distributed on 5¼ and 3½ floppy disks
Windows 3.x 3½ Floppy (720 KB, 1.2 MB, and 1.44 MB floppy)
Windows 95 Distributed on CD-ROM media (ROM = Read Only Media, new data cannot be written/burned to) (Boot floppy disk may or may not be required) Max Capacity of CD-ROM 737MB
Windows 98 / 98 SE (Second Edition) / (Boot floppy disk may or may not be required) Distributed on CD-ROM media (Boot floppy disk may or may not be required)
Windows ME Distributed on CD-ROM media
Windows XP Distributed on CD-ROM media (474MB XP Home 2001Beta version, 589MB XP Pro with SP3)
Windows Vista Distributed on DVD media (4.7GB Decimal or 4.37 binary max capacity) Note that Windows does not require the full capacity of a DVD. Some computer manufactures may also include free trial versions of MS Office, Anti-Virus software and other software or utilities.
Windows 7 Distributed on DVD media
Windows 8/8.1 Distributed on DVD media
Windows 10 Distributed on USB Flash drive (6GB Write protected) media Also available as an .ISO download which can be used to create installation media using either a DVD or a 6 to 8GB USB Flash drive. Note that more recent versions of Windows 10 may require a larger USB drive.