SINIX is a discontinued variant of the Unix operating system from Siemens Nixdorf Informationssysteme. SINIX supersedes SIRM OS and Pyramid Technology's DC/OSx. Following X/Open's acceptance that its requirements for the use of the UNIX trademark were met, version 5.44 and subsequent releases were published as Reliant UNIX by Fujitsu Siemens Computers.

In some versions of SINIX (5.2x) the user could emulate the behaviour of a number of different versions of Unix (known as universes). These included System V.3, System III or BSD. Each universe had its own command set, libraries and header files.

The original SINIX was a modified version of Xenix and ran on Intel 80186 processors. For some years Siemens used the NSC-32x32 (up to Sinix 5.2x) and Intel 80486 CPUs (Sinix 5.4x - non MIPS) in their MX-Series.

Later versions of SINIX based on System V were designed for the:

• SNI RM-200, RM-300, RM-400 and RM-600 servers running on the MIPS processor (SINIX-N, SINIX-O, SINIX-P, SINIX-Y)
• SNI PC-MX2, MX300-05/-10/-15/-30, Siemens MX500-75/-85 running NS320xx (SINIX-H)
• PC-MXi, MX300-45 on the Intel X86 processor (SINIX-L)
• SNI WX-200 and other IBM-compatible i386 PCs on the Intel 80386 and newer processors (SINIX-Z)

The last release under the SINIX name was version 5.43 in 1995.

The last Reliant UNIX versions were registered as UNIX 95 compliant (XPG4 hard branding).

The last release of Reliant UNIX was version 5.45.

• BS2000
• VM2000

• Siemens Business Services - SINIX patches and support
• The SINIX operating system
• Sven Mascheck, SINIX V5.20 Universes