About the Unix family

it was originally developed at AT&T as a multitasking system for minicomputers and mainframes in the 1970’s it has since grown to become one of the most widely-used operating systems anywhere two major variation: System V (Unix System laboratories, USL) and Berkeley Software Distribution (BSD Unix) then many other flavours of these two (Solaris, AIX, Linux, ...) the POSIX standardization by IEEE can be seen also as a third Unix variation