interaction with computers was primarily by means of command-line interfaces, initially on machines like the Teletype Model 33 ASR, but then on early CRT-based computer terminals such as the VT52. All of these devices were purely text based, with no ability to display graphic or pictures. For business application programs, text-based menus were used, but for more general interaction the command line was the interface. Around 1964 Louis Pouzin introduced the concept and the name shell in Multics, building on earlier, simpler facilities in the Compatible Time-Sharing System (CTSS). From the early 1970s the Unix operating system adapted the concept of a powerful command-line environment, and introduced the ability to pipe the output of one command in as input to another. Unix also had the capability to save and re-run strings of commands as "shell scripts" which acted like custom commands. The command-line was also the main interface for the early home computers such as the Commodore PET, Apple II and BBC Micro – almost always in the form of a BASIC interpreter. When more powerful business oriented microcomputers arrived with CP/M and later DOS computers such as the IBM PC, the command-line began to borrow some of the syntax and features of the Unix shells such as globbing and piping of output. The command-line was first seriously challenged by the PARC GUI approach used in the 1983 Apple Lisa and the 1984 Apple Macintosh. A few computer users used GUIs such as GEOS and Windows 3.1 but the majority of IBM PC users did not replace their COMMAND.COM shell with a GUI until Windows 95 was released in 1995. Modern usage as an operating system shell While most non-expert computer users now use a GUI almost exclusively, more advanced users have access to powerful command-line environments: The default VAX/VMS command shell, using the DCL language, has been ported to Windows systems at least three times, including PC-DCL and Acceler8 DCL Lite. Unix command shells have been ported to VMS and DOS/Windows 95 and Windows NT types of operating systems. COMMAND.COM is the command-line interpreter of MS-DOS, IBM PC DOS, and clones such as DR-DOS, SISNE plus, PTS-DOS, ROM-DOS, and FreeDOS. Windows Resource Kit and Windows Services for UNIX include Korn and the Bourne shells along with a Perl interpreter (Services for UNIX contains ActiveState ActivePerl in later versions and Interix for versions 1 and 2 and a shell compiled