Released to compete with the Nintendo Entertainment System, the Master System was an 8-bit console which was more powerful yet failed to break Nintendo's market dominance. It was generally regarded as a failure in the USA, but in Europe, Australasia and Brazil it was highly successful - so much so that one can still buy one in Brazil despite the system's age.
Three different models of the Master System were produced - the Master System, Master System II and Master System III (the third being released only in Brazil). All three were capable of running the same software and were, more or less, the same machine. However, there were key differences between them, particularly the first and second.
The original Master System was capable of accepting software on the standard cartridges, but also on special "Sega Cards". Only one game is known to have been Card-exclusive, Hang On. It also sported a reset button. These features were both lacking on the Master System II,
CPU: An 8-bit Zilog-80 running at 3.6Mhz
RAM: 8kb Internal Memory, 16kb Video Memory
Screen Resolution: 256 x 192
Maximum on-screen colours: 32 on-screen, total of 64
Sound Channels: 4 Mono
Control Pad: Went through at least three different version, all simple affairs involving a pad and two buttons. Surprisingly durable and more than capable.
3D Glasses: Still considered a wonder by today's standards. Only supported by a few games, but very well done. Because they used the Card interface, they only work on the original Master System.
Light Phaser: The NES had the Zapper, a rather nice little lightgun which was perfect for shooting ducks. On-screen, at least. The Master System had just as nice a gun in the form of a Light Phaser. Of course, it was only supported by a few games, but was excellent nonetheless.