Richard Stallman Mellon's Mach microkernel in a project called GNU Hurd, which has yet to achieve the maturity level required for full POSIX compliance. In 1991, Linus Torvalds, a Finnish student, used the GNU's development tools to produce the free monolithic Linux kernel. The existing programs from the GNU project were readily ported to run on the resultant platform. Most sources use the name "Linux" to refer to the general-purpose operating system thus formed, while Stallman and the FSF call it "GNU/Linux". This has been a longstanding naming controversy in the free software community. Stallman argues that not using GNU in the
Operating system existing hardware production. MCP is still in use today in the Unisys ClearPath/MCP line of computers. UNIVAC, the first commercial computer manufacturer, produced a series of EXEC operating systems. Like all early main-frame systems, this batch-oriented system managed magnetic drums, disks, card readers and line printers. In the 1970s, UNIVAC produced the Real-Time Basic (RTB) system to support large-scale time sharing, also patterned after the Dartmouth BC system. General Electric and MIT developed General Electric Comprehensive Operating Supervisor (GECOS), which introduced the concept of ringed security privilege levels. After acquisition by Honeywell it was renamed General Comprehensive Operating System (GCOS).