GCOS!
        
        
        GCOS is the collective name for a group of mostly-unrelated operating systems
        from GE, Honeywell, and Bull/Atos. GCOSes run on systems ranging from the
        Level 61 small business minicomputer to large mainframes like the DPS
        9000/TA300.
        
        GCOS 61: Long-dead OS for the Level 61 system inherited from Bull. Primitive.
        
        GCOS 62 (GCOS 4): Minicomputer OS. EOL'd in Bull's markets in the late 1980s,
        but a variant is still sold by NEC (under emulation) as ACOS-2.
        
        Level 6 (GCOS 6): Minicomputer OS. Multics-like command shell. Sold for both
        technical/control workloads and business workloads. Killed circa 1991 and
        migrated to an AIX-based emulation environment, HVX.
        
        Level 64 (GCOS 7): Entry mainframe ("midframe") OS. 32-bit, EBCDIC, and has a
        robust UNIX environment (which also provides services for TCP/IP.) Large but
        declining customer base in Western Europe, almost none in the US. NEC sells a
        variant as ACOS-4, running on custom CISC CPUs; Bull's own systems were
        moved to emulation on x86 and Itanium systems around 2001.
        
        Level 66 (GCOS 8): The high end of the GCOS family. Originated at GE circa
        1962, runs on 36-bit mainframes (until ~2006) and under emulation on Itanium.
        GCOS 8 still has customers in both America and Europe. NEC sold a variant as
        ACOS-6 after inheriting Toshiba's mainframe customer base, but mostly
        abandoned 36-bit systems through the 1990s and repositioned ACOS-4 as the top
        end of their product family.
        
 (TXT)  A writeup I did on GCOS 8 history, hosted with permission at linkerror.com
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