GMC-4

The GMC-4 is the only 4-bit microcomputer to be mass-produced in the last 30 years. It was produced by Gakken, a Japanese publisher who distributed it with a magazine attached to a box containing the components required to assemble the computer.

The purpose of the GMC-4 is education. It provides an accessible way to learn about assembly language and the principles of computing.

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SOS

SOS is the international Morse code distress signal (· · · – – – · · ·). This distress signal was first adopted by the German government in radio regulations effective April 1, 1905, and became the worldwide standard under the second International Radiotelegraphic Convention, which was signed on November 3, 1906, and became effective on July 1, 1908. SOS remained the maritime radio distress signal until 1999, when it was replaced by the Global Maritime Distress and Safety System. SOS is still recognized as a visual distress signal.

The SOS distress signal is a continuous sequence of three dits, three dahs, and three dits, all run together without letter spacing. In International Morse Code, three dits form the letter S, and three dahs make the letter O, so "SOS" became an easy way to remember the order of the dits and dahs. In modern terminology, SOS is a Morse "procedural signal" or "prosign", and the formal way to write it is with a bar above the letters: SOS.

In popular usage, SOS became associated with such phrases as "Save Our Ship" or "Save Our Souls" or "Send Out Succour". SOS is only one of several ways that the combination could have been written; VTB, for example, would produce exactly the same sound, but SOS was chosen to describe this combination. SOS is the only nine-element signal in Morse code, making it more easily recognizable, as no other symbol uses more than eight elements.

SOS (Rihanna song)

"SOS" is a song by Barbadian singer Rihanna from her second studio album A Girl like Me (2006). It was written by Jonathan "J.R." Rotem, E. Kidd Bogart and Ed Cobb, with production was handled by Rotem, Carl Sturken and Evan Rogers. It was released on February 14, 2006, as the lead single from the album. "SOS" is a dance song which samples taken from Some Bizarre Records Track titled Tainted Love artist PKA Soft Cell, a song written by Cobb in 1965 and popularised by Soft Cell in 1981. Critical reception of "SOS" was generally positive, with the majority of music critics praising the inclusion of the "Tainted Love" sample. Some critics compared "SOS" to Rihanna's debut single, "Pon de Replay" (Music of the Sun, 2005).

"SOS" became a commercial success. In the United States, it topped the Billboard Hot 100 chart for three consecutive weeks, becoming Rihanna's first number one single on the chart. "SOS" peaked at number one on the US Hot Dance Club Songs chart and Mainstream Top 40 chart. "SOS" was certified Platinum by the Recording Industry Association of America for shipments of over 1,000,000 copies. The song was also successful in Europe as well as Australia, where it spent eight consecutive weeks at number one.

21st Special Operations Squadron

The 21st Special Operations Squadron is a unit within the 352d Special Operations Group (352 SOG), United States Air Force, United States European Command, and was based at Royal Air Force base RAF Mildenhall in Suffolk, eastern England.

Mission

The 21st Special Operations Squadron, which fell under the 352nd Special Operations Group, RAF Mildenhall, UK, was inactivated on 31 October 2007 with the inactivation ceremony taking place at RAF Mildenhall, UK on 9 October temporarily ending the Air Force Special Operations vertical lift mission in Europe.

The inactivation of the Dust Devils was the first step in preparation for the arrival of the CV-22 tilt-rotor aircraft.

The 21st Special Operations Squadron's mission consisted of day or night, all-weather, low-level penetration of denied territory to provide infiltration, exfiltration, resupply, or fire support for elite air, ground, and naval forces. The unique capabilities of the MH-53J permitted the squadron to operate from unprepared landing zones.