Early mainframe games  Mainframe computers are computers used primarily by businesses and academic institutions for large-scale processes. Before personal computers, first termed microcomputers, became widely available to the general public in the 1970s, the computing industry was composed of mainframe computers and the relatively smaller and cheaper minicomputer variant. During the mid to late 1960s, many early video games were programmed on these computers. Developed prior to the rise of the commercial video game industry in the early 1970s, these early mainframe games were generally written by students or employees at large corporations in a machine or assembly language that could only be understood by the specific machine or computer type they were developed on. While many of these games were lost as older computers were discontinued, some of them were ported to high-level computer languages like BASIC, had expanded versions later released for personal computers, or were recreated for bulletin board systems years later, thus influencing future games and developers. Early computer games began to be created in the 1950s, and the steady increase in the number and abilities of computers over time led to the gradual loosening of restrictions on access to mainframe computers at academic and corporate institutions beginning in the 1960s. This in turn led to a modest proliferation of generally small, text-based games on mainframe computers, with increasing complexity towards the end of the decade. While games continued to be developed on mainframes and minicomputers through the 1970s, the rise of personal computers and the spread of high-level programming languages meant that later games were generally intended to or were capable of being run on personal computers, even when developed on a mainframe. These early games include "Hamurabi", an antecedent of the strategy and city-building genres; "Lunar Lander", which inspired numerous recreations in the 1970s and 1980s; "Civil War", an early war simulation game; "Star Trek", which was widely ported, expanded, and spread for decades after; "Space Travel", which played a role in the creation of the Unix operating system; and "Baseball", an early sports game and the first baseball game to allow player control during a game. Mainframe computers are powerful computers used primarily by large organizations for computational work, especially large-scale, multi-user processes. The term originally referred to the large cabinets called "main frames" that housed the central processing unit and main memory of early computers. Prior to the rise of personal computers, first termed microcomputers, in the 1970s, they were the primary type of computer in use, and at the beginning of the 1960s they were the only type of computer available for public purchase.