Which Windows version first introduced multi-monitor support?

Windows 98 was the first Windows version to introduce built-in multi-monitor support.

Released to retail on June 25, 1998, Windows 98 added support for using several physical displays with one PC. The feature was aimed at users who needed a larger desktop workspace, such as professionals working with graphics, spreadsheets, or multiple applications.

Windows 98 could support as many as nine monitors, although each display generally required its own PCI graphics adapter. This was not the same as simply mirroring one screen: Windows could extend the desktop across the connected displays, allowing windows to be moved between them.

Windows 95 is the common mix-up because it preceded Windows 98 and supported many important hardware improvements. However, native multi-monitor support is specifically listed among Windows 98's new capabilities. Windows 98 Second Edition, released on June 10, 1999, refined the original system but did not change which Windows release first introduced the feature.