BESYS

BESYS (Bell Operating System)
Developer	Bell Labs
Written in	IBM's FORTRAN and North American's Symbolic Assembly Program (SAP)
Working state	Discontinued
Initial release	1957
Latest release	BE90 / 1968
Platforms	IBM 704

BESYS (Bell Operating System) was an early computing environment originally implemented as a batch processing operating system in 1957 at Bell Labs for the IBM 704 computer.

History of IBM mainframe operating systems
Early mainframe computer OSes GM OS & GM-NAA I/O (1955) BESYS (1957) UMES (1958) SOS (1959) IBSYS (1960) MIT CTSS (1961) 7040/7044 Operating System (16/32K) (7040-PR-150) 1410/7010 Operating System (1410-PR-155)
Miscellaneous S/360 line OSes BOS/360 (1965) TOS/360 (1965) TSS/360 (1967) MTS (1967) ORVYL (1967) RACS (1965) RAX (1966) MUSIC (1972) MUSIC/SP (1985)
DOS/360 and successors (1966) DOS/360 (1965) DOS/VS (1972) DOS/VSE (1979) VSE/AF (1979) VSE/SP (1983, 1985) VSE/ESA (1991) z/VSE (2005) VSEⁿ (2021)
OS/360 and successors (1966) MFT (1966) MFT II (1968) OS/VS1 (1972) OS/VS1 BPE MVT (1967) 65MP OS/VS2R1 (SVS) (1972) MVS (OS/VS2R2 and later) (1974) MVS/SE (1978) MVS/SE 2 (1979) MVS/SP Version 1 (1980) MVS/XA (1983) MVS/ESA (1988) OS/390 (1995) z/OS (2000)
VM line CP-40 /CMS (1967) CP-67 /CMS (1967) VP/CSS (1968) VM/370 (1972) VM/BSE (BSEPP) VM/SE (SEPP) VM/SP (1980) VM/XA MA (1984) VM/XA SF (1985) VM/XA SP (1988) VM/ESA (1990) z/VM (2000)
TPF line ACP (1967) TPF (1979) z/TPF (2005)
UNIX and Unix-like UTS (1981) AIX/370 (1990) AIX/ESA (1991) MVS/ESA OpenEdition (1993) VM/ESA OpenEdition (1995) OS/390 UNIX System Services (1996) Linux (1999) z/VM OpenExtensions (2000) z/OS UNIX System Services (2001) OpenSolaris (2008)