The most difficult in­for­mat­ics riddles

Dennis Ritchie and Ken Thompson wrote the original UNIX in 1969 and early 1970 at AT&T Bell Labs research centre. It gained quick adoption in academia and business, and evolved into a family of both proprietary and free related versions and clones. Linux, Android, Mac OS X and iOS are also its derivatives.

The service consisting in sending text messages between computers was invented in 1971 by Ray Tomlinson. Previously, mail could be sent only to others who used the same computer. To achieve this,"Ray" he used the @ sign to separate the user name from the name of their machine, a scheme which has been used in email addresses ever since.

USB - short for Universal Serial Bus, is an industry standard that defines cables, connectors and communications protocols for connection, communication, and power supply between computers and devices.