The SG-1000 Mark III is a console made by Sega.
The SG-1000 Mark III was released in Japan in 1984 to compete with the Nintendo Family Computer. It came after the SG-1000 Mark I and SG-1000 Mark II. It was introduced in 1984 in Japan, and was built similar to the Mark II. The insides are akin to that of an MSX, and the Mark I, but had some improvements. The system also used Sega cards and earlier SG-1000 titles. The cards are exactly the same ones in the SG-1000 Mark II card catcher add-on. The said add-on was built in the Mark III.
The system had been redesigned as the Sega Master System for its release in other Markets. The Master System I later came back to Japan.
Neither the Mark III or the Master System I had much success dealing with the Nintendo Famicom.