Windows NT 3.1 build 340

{Infobox Windows build }}
 * build of = Windows NT 3.1
 * image = WindowsNT3.1-3.1.340-Desktop.png
 * buildtag = 3.1.340.1
 * arch = x86
 * sku = Workstation Advanced Server
 * compiled = 1992-10-12
 * winver = WindowsNT3.1-3.1.340-About.png
 * rivals=

Windows NT 3.1 build 340.1 is the October 1992 pre-release build of Windows NT 3.1, available in both Workstation and Advanced Server editions. The latter was leaked on 3 November 2017 by The Distractor on BetaArchive. It is the earliest leaked build of the Advanced Server version of Windows NT, at the time still called "LAN Manager for Windows NT".

This build is often mislabeled either as build 319.1 or 328.1, which are actually file versions of its kernel files ( and  ). NTFS now works in this build.

Around the release of this build, the now well-known error in the processor detection routine appeared, preventing installation on the Pentium II and later without modification. It made its way into the final release and persisted into Windows NT 3.5. It was finally fixed around Windows NT 3.51 build 1002.1.

This is the first known build to change the desktop background color from grey to teal. This change would later carry over to Windows 95. Also, this is the first build to have an option to create an Emergency Repair Diskette, in some places also prelimary named "Emergency Maintenance Diskette".

File differences
The following files have been introduced or removed compared to build 297: