Transaction Management eXecutive or TMX was NCR Corporation's proprietary transaction processing system^[1] running on NCR Tower 5000-series systems which were based on Motorola 680xx CPUs. This system was used mainly by financial institutions in the 1980s and 1990s.

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Basic features of the TMX operating system are listed below:

• It was a multiuser, multitasking 32-bit operating system.
• It featured a proprietary network called LBN (Local Branch Network).
• Later versions of TMX had Token Ring support which was called LBN Emulation.
• It had device support for financial applications on LBN, e.g. NCR dumb terminals, passbook printers, cash dispensers, magnetic stripe reader and pinpad.
• It contained SNA LU emulations for mainframe connectivity.
• Peripheral device configuration was fixed during boot time. Configuration changes were made using the SYSGEN command.
• It supported a flat file system; there were no subdirectories. File name format was like this: diskname:usernumber.catalogname.filename.ext;version
• Files had various types, like text files and index sequential data files.
• Main programming language was Whitesmiths C, but the compiler was not ANSI C compliant.
• It had limited memory (several MB) and disk (several hundred MB).

NCR Tower 5000 systems were also capable of running UNIX SVR3 version.