The Sega SG-1000 was Sega's first home video game console. It was the predecessor and foundations of the Master System. The 'S' and the 'G' stand for 'Sega Game'. It was marketed only in Japan, and was released in July 15, 1983, but was later marketed on another company in Australia and New Zealand. It wasn't extremely popular, and was behind almost every console released at the time. There were two models of the Sega SG-1000 made, before the updated third model came out, with updated graphics and RAM.
The console was released on the same day as Nintendo's Famicom. Grandstand released the console in New Zealand. There were a slew of clones released that could play SG-1000 games. The console was the basis of the more successful Master System, from Sega.
 Models and Hardware
There were three different models of the SG-1000 released. The Mark I was the first model, with white/beige casing, blue stickers, and a cartridge slot in the middle of the console. The controllers were joysticks. The Mark II was released later, and the cartridge slot was on the top-right hand side of the console, and instead of a joystick, there were control pads. The Mark III was the real success for the SG-1000, with increased RAM, graphics, and color palette.
The computer variant of the SG-1000 was the Sega SC-3000, the 'S' and 'C' standing for Sega Computer.
The console took cartridges of the same shape as the Colecovision, unlike the Master System game cartridges. The Sega Card Catchers were the MyCard / Sega Card variant for the SG-1000.