You can never have too many processors

Sega’s fifth generation console, and a complex beast of a machine – eight processors all working in tandem.

Processor 1 & 2: Dual Hitachi SH2 processors, these act as the central processing unit of the whole system, and are based on the Hitachi SuperH RISC design and are arranged in a master/slave fashion (Or a master/servant) The idea was for both CPU to work co-operatively which would help increase performance for games. Sega had already used multiple CPU’s for the 32X and in their arcade boards.
In practice however this was far from ideal, as many third party developers were not accustomed to using the second CPU, and the way Sega implemented it was far from ideal. You see they share the same memory bus which means one CPU can access the main Ram at a time, limited performance and having the SH2 rely in its internal cache at lot more. Plus with the added complexity of keeping both CPU’s occupied and in sync with each other was a lot more of a challenge, and to top it off Sega’s own software libraries were poor in comparison to the competition. It was some time into the Saturn’s lifecycle that the development tools were on the level that rivalled the PlayStation.

Processor 3: Hitachi SH1, a dedicated CPU for the CD-ROM system, this handles access and control, in addition to security. Running at round 20Mhz this was rather overkill for its task but did mean the Saturn has relatively short loading times compared to the PlayStation and on par with the 3DO.

Processor 4: Saturn/System Control Unit, Kinds of like the chipset of the system, it handles communications for all the core processors of the Saturn, and also contains a DSP/VLIW processor which helps out in the 3D rendering, before the VDP1 takes over. There’s also a DMA controller to manage access to the main RAM

Processor 5: VDP1, Video Display Processor 1, a continuation from the VDP from the Megadrive design and from their System 32 arcade sprite scaling hardware. This is responsible for the foreground graphics, sprite and the 3D effects of the Saturn

Processor 6: VDP2, similar as VDP1 but for the background elements.

Processor 7: SCSP, Saturn Custom Sound Processor, the sound processor which is responsible for the MIDI decoding and for compressed CD Audio

Processor 8: Motorola 68EC00, the sound CPU, feeds commands and helps out with the sound processing

That’s a lot of processors, unfortunately many games didn’t utilise all the processors with the second CPU being idle for the majority of third party games.
Unlike the PlayStation, Sega didn’t integrate the processors well with the PlayStation having its MIPS CPU, GTE and MJPEG decoder all on one chip, whilst each processor in the Saturn was on its own chip and the mainboard had to be designed around that, which made the Saturn expensive to produce. Sega did revise the board to reduce the amount of separate chips to help with the manufacturing cost.

From the first look of the components you would think there would be some Sega Megadrive compatibility since it has the 68000, VDP and the SCSP with shares the same similarity with the Yamaha sound chip from the mega drive. Only processor is missing is the Zilog, which could be emulated instead on one of the SH2 processors. Unfortunately there is not backwards compatibility with its predecessor at all, considering it had a respectable market share with many users looking to upgrade whilst keeping their existing game library playable on the new machine, you would think Sega would have invested in a backwards compatibility solution. Maybe the VDP’s were too different?

Memory

Like the processors, the memory on the Saturn was also fragmented to hell, with many different pools of RAM accessible by the different processors:
2MB System Memory
1MB of this is SDRAM
The other 1MB of this is DRAM, which is slower
1.5MB Video memory
512Kb of this is for the framebuffer of VDP1, split into 2x 256Kb
Another 512Kb is dedicated to VDP1
Another 512Kb is for VDP2
512Kb Sound RAM for the SCSP
512Kb for the SuperH1 CD-ROM CPU

Comparisons

Although the Saturn has several distinct advantages compared to the Sony PlayStation, the multiple processors and the low clock speed of each processor made harnessing the power very difficult, with Saturn ports taking longer to develop for and were in most cases inferior to the Playstation versions, which was the case for many 3D titles. For 2D game the Saturn could match or even exceed the PlayStation version due to the Saturn sprite capabilities. Another factor was the maturity of the PlayStations software libraries which enabled developers to use C instead of assembler, until Sega revised their SDK’s.
Another common difference between the PlayStation, and the Nintendo 64 was the Saturn’s use of quadrilaterals, where polygons are rendered using four points, rather then the three used on the other consoles (except 3DO which was also quad based), this was due to the arcade Model 2 also using quads to render its graphics, and Sega wanted to ensure games could be ported from Model 2 to Saturn as easy as possible. Its not fair to say Sega made a bad decision since at the time of the Saturn’s release (1994), both methods were equally as popular and there was no industry standard set (PC graphic accelerators were barley a thing also). It wasn’t until OpenGL and DirectX was standardised, and the release of the Nintendo 64 where triangles were the accepted form of 3D graphics.

System Software

Saturn easily had the best BIOS/System firmware of all the fifth generation systems, with a nice CD player that was able to manipulate the sound in real-time and had a bonus space themes visualizer. It was also the only console if its generation to feature a real time clock, except for the N64 DD (Not the base N64)

Controllers

The Saturn features two controller ports, with the option of a multitap being used to expand for up to 6 players on one port, for a total of 12 for each console.
A standard controller was included with the Saturn, this had six face buttons, two shoulder buttons, a directional pad and the start button. It was not backwards compatible with the MegaDrive and was a new design.
A controller with an analogue control was introduced later, known as the 3D pad which allowed for analogue control, similar to the analogue stick on the Nintendo 64. This was dependant on the support of the game itself, many games did not take advantage as it was not a standard accessory.

Expansion

The slot above the CD-ROM lid is used to insert expansion cartridges which can enhance the Saturn’s functionality, one of these was a backup memory cartridge with allowed for game saved to be moved to the cartridge to make space on the Saturn’s internal memory. Some (not all) games can even save directly on the cartridge itself, instead of having to manually move the file.
Being able to backup your saves was crucial since the Saturn used RAM for storage, which relies on a 2032 battery being present. If this looses charge then the memory is wiped and the saves are lost.
Third party accessories include the Action Replay which allows for cheat code to be used in the game,
In Japan, Ram cartridges could expand the consoles DRAM, allowing for more detailed graphics. Sadly this was never released in Europe/US.

The other expansion slot

There was also an expansion slot at the back of the Saturn which was only used for the MPEG upgrade card, which allowed the Saturn to decode full resolution MPEG1 (Not MPEG2 that DVD or DVB TV uses). Its possible the later 64X would have gone here.

Communications Port

Used to link 2 Saturn’s together for enhanced multi player, not widely supported.

Addons

Like the Megadrive Sega also wanted to expand the system several times, one of which was a 64X like addon that would have integrated a Real3D graphics processor which would have given graphics in between Model 2/3 arcade systems.
Nvidia were also considered for a graphics upgrade hardware, having worked with Sega with the NV1 graphics processor, but again this never came to light.
Perhaps it was for the best that these addons were never released, and that Sega hit the reset button with the Dreamcast instead. The Saturn was a mess of processors, and adding more would have complicated the issue even more, plus it looks bad that you need an addon in order to match the rival consoles, even when your console is more expensive than the competitors.
Its worth mentioning that the 64X was never officially announced by Sega,

ST-V

The arcade version of the Saturn, designed for use with third-party developers who wanted to release their games in the arcade with the option for a Saturn port at some point, is also used for low end cheaper games due to the high cost of Sega’s Model 2 board. It is exactly the same as the Saturn but used cartridges rather than the CD-ROM which eliminates loading times.

Games