Windows NT 3.5 is a major release of the Windows NT operating system developed by Microsoft and oriented towards businesses. It was released on September 21, 1994, as the successor to Windows NT 3.1 and the predecessor to Windows NT 3.51.
|A version of the Windows NT operating system|
|Source model||Closed source|
|Released to |
|September 21, 1994|
|Latest release||Service Pack 3 (3.5.807) / June 21, 1995|
|Platforms||IA-32, Alpha, MIPS, PowerPC|
|Userland||Windows API, NTVDM, OS/2 1.x, POSIX.1|
|License||Commercial proprietary software|
|Preceded by||Windows NT 3.1 (1993)|
|Succeeded by||Windows NT 3.51 (1995)|
|Unsupported as of December 31, 2001|
One of the primary goals during Windows NT 3.5 development was to improve the operating system's performance. As a result, the project was codenamed "Daytona", after the Daytona International Speedway in Daytona Beach, Florida.
On December 31, 2001, Microsoft declared Windows NT 3.5 obsolete and stopped providing support and updates for the system.
Windows NT 3.5 comes in two editions: NT Workstation and NT Server. They respectively replace the NT and NT Advanced Server editions of Windows NT 3.1. The Workstation edition allows only 10 concurrent clients to access the file server and does not support Mac clients.
Windows NT 3.5 includes integrated Winsock and TCP/IP support. (Its predecessor, Windows NT 3.1, only includes an incomplete implementation of TCP/IP based on the AT&T UNIX System V "STREAMS" API.) TCP/IP and IPX/SPX stacks in Windows NT 3.5 are rewritten. NetBIOS over TCP/IP (NetBT) support as a compatibility layer for TCP/IP was introduced as also the Microsoft DHCP and WINS clients and DHCP and WINS servers.
Windows NT 3.5 can share files via the File Transfer Protocol, and printers through the Line Printer Daemon protocol. It can act as a Gopher, HTTP, or WAIS server, and includes Remote Access Service for remote dial-up modem access to LAN services using either SLIP or PPP protocols. Windows NT 3.5 Resource Kit includes the first implementation of Microsoft DNS.
Other new features in Windows NT 3.5 include support for the VFAT file system, Object Linking and Embedding (OLE) version 2.0 and support for input/output completion ports. Microsoft updated the graphical user interface to be consistent with that of Windows for Workgroups 3.11. NT 3.5 shows performance improvements over NT 3.1, and requires less memory.
In May 2020, the full source code for the second release candidate build (build 782.1) of Windows NT 3.5, along with source code for the original Xbox leaked onto the Internet. Microsoft stated it had nothing to share about the leaks. 
The first release of Windows NT was larger and slower than expected, so the next major push was a project called "Daytona", named after the speedway in Florida. The main goals for this release were to reduce the size of the system, increase the speed of the system, and, of course, to make it more reliable.