Windows 4.x

Windows 4.xx (codenamed Cougar) can refer to either an individual or following versions of Microsoft Windows.
 * Windows 4.00 (codenamed Cougar/Chicago/Cairo/Hydra)
 * Windows 4.01 (codenamed Cleveland/Nashville)
 * Windows 4.10 (codenamed Memphis)
 * Windows 4.90 (codenamed Georgia/Millenium)