Despite what many remember, it wasn’t just ‘NES vs Master System’ in the 80s.
Sega had multiple attempts at the 8-bit wars.
Released only in Japan and New Zealand, Sega’s first console is essentially a Colecovision and MSX hardware wise, having the exact same specs. Unfortunately for Sega, it launched the exact same day as a much more advanced console you may have heard of, the Nintendo Family Computer.
There are three models:
‘Germany’ edition - the first Japanese model
Red/Blue - The most common edition
The extremely rare New Zealand Sega 1000 console distributed by Grandstand. Probably the rarest of all Sega consoles.
An older style console design, it has Atari-shape carts and Atari-like packaging
It was also re-launched one year later 1984 as the SG1000 II in Japan with more Famicom style styling and Famicom style controllers.
This was also where Sega cards were introduced, PC Engine style game cards which were cheaper than carts. SG1000 hardware needed a pin converter to play them, called the Card Catcher.
The Home PC version of the SG1000 with the keyboard built in, as Sega’s MSX equivalent. Released in Japan, Australia, New Zealand and Europe in various colours. Many PC accessories like printers came along with it.
Sega Mark III
Not truly a generational leap, the 1985 (only two years later!) Mark III is an SG1000 with some extra chips and an extra video mode, specifically designed to match or exceed the Famicom technically, which it does in many ways but still falls short in others, largely due to the SG1000 heritage. It also now supported cards natively, and had full SG1000 compatibility.
Games came in shiny gold boxes with typically very nice artwork.
In my opinion, it’s the best looking Sega hardware ever.
Mark III FM
Released separately, you could upgrade the Mark III with an FM module
This added FM audio to games, making them sound a lot more advanced, more like a typical arcade game of the era. Games had to support it specifically, but a large number of games did, including games never released in Japan. See here for more info and a list of supported games:
The Sega System/Master System/Power Base
Finally released in the west in 1986/1987, the Mark III was redesigned into a larger monolith-like black block, without the FM sound.
It changed the cart shape to be more like Famicom carts, and they came in a signature ‘white with grid’ box design, likely designed to contrast the Nintendo black box ‘pixel art’ design. Western box art is legendary for some… questionable quality artwork.
Despite it later being branded as the Master System, the western release originally made no reference to the Master System name as the name of the platform.
The branding was a bit of a mess, marketing and games simply called it ‘The Sega’ and the basic set was released as ‘The Sega Base System’
A pack with gun included was sold as ‘The Master System’ - seemingly making ‘Master System’ an equivalent of the NES ‘Action Set’.
But yet the console said ‘Master System/Power Base’ on the front, seemingly making both ‘Master System’ and ‘Power Base’ the equivalents of the name of the core console element - equivalent of the NES ‘Control Deck’.
By the time of the PAL releases it has settled down to being known as the Master System and a few years later games started having Master System branding to make a distinction from Mega Drive/Genesis games.
Japanese Master System
It looks like the western Sega, with the FM unit built in, but this time is clearly branded 'Master System’ (which makes sense here as it’s a ‘final’ system with all formats supported and FM audio built in.
Master System II and Brazilian releases
The (now clearly branded) Master System lived on after the launch of the Mega Drive as a cheaper, feature-incomplete (no card support, no 3D support, no FM possible, RF-only output, cheaper plastic and smaller, very rounded 90s-looking redesign) budget system for kids in Australia, NZ, Europe and Brazil.
Not really covered in this thread as it has its own thread, but the Game Gear is just base Mark III hardware with an increased colour pallette and reduced screen resolution.
Interestingly, just like the Mark III being an upgraded SG1000, the Mega Drive is basically a revision of the Mark III with some extra chips. It contains the entire Mark III/MS chipset, with some additional chips from the Sega System 16 arcade board. As such it has hardware compatibility, which can be triggered by a simple cart converter which disables the additional chips.