In 1973, AT&T released Version 5 Unix and licensed it to educational institutions, and licensed 1975's Version 6 to companies for the first time. While commercial users were rare because of the cost, the latter was the most widely used version into the early 1980s. Anyone could purchase a license, but the terms were very restrictive; licensees only received the source code, on an as-is basis. The licenses also included the machine-dependent parts of the kernel, written in PDP-11 assembly language. Copies of the "Lions' Commentary on UNIX 6th Edition, with Source Code" circulated widely, which led to considerable use of Unix as an educational example. The first meeting of Unix users took place in New York in 1974, attracting a few dozen people; this would later grow into the USENIX organization. The importance of the user group stemmed from the fact that Unix was entirely unsupported by AT&T.