Here we have the DVI-I layout from Wikipedia. I've sort of abused the PNG generation algorithm (changing the number before "px" in address bar) and I shall present you a 3840 pixels wide version:
3 monitors from 1 connector
In school I have been told that theoretically there can be 3 monitors connected over DVI-I, one of them being analog. However I haven't found any 3-way hub being sold which would end with 2 DVI-Ds and one D-SUB (known as VGA, but Vertical Graphics Array is not the transmission technology itself). The D-SUB could be connected to a passive DVI to D-SUB converter to produce some slightly differently colored 3rd digital output.
Analog audio and digital video
Those obscure pins for analog output could also have another use - to transfer analog sound, up to distinct 5.1 or 7.1 without explicit sound for center speakers:
Red front L + R,
Green back L + R,
Blue Center + Subwoofer or
middle L + R, with:
All Center + Subwoofer
This might be diverged too into audio jacks, instead of being played by one of those shitty tweeter speakers integrated in the monitor. At least it would bypass the even more shitty DAC. This would unfortunately require to write a driver for it to be output and to hack the monitor firmware to receive it properly, but who the hell would expect a monitor to produce an satisfactory sound? There are 5.1 speakers for that purpose. Anyway, still better than PC Speaker.
The pins could be also misconnected to a monitor in order to produce an technically interesting sound visualization. And someone needs to write a driver for this.
Digital audio and analog video
Do you remember your homemade Covox? If you don't know what it is, then you are most probably not an 80's kid. Even I, late 90's kid know what it is, but only because I have interest in the demoscene, of which I haven't recently known, how deep underground culture it actually is.
Anyway, the Covox Speech Thing, as well as the more advanced version of it, Disney Sound Source, worked on a very simple method of converting audio played on 8-bit bus by ladder DAC, having the least significant pin assigned 2 resistors and merging it with the sequentially more significant bits, which have also 2 resistors. The last resistor for each bit is common with all the previous signal, creating some kind of merging L routes for the electric current. At the end, there might be one more resistor and a condenser for amplification and DC offset correction.
And all this has to do with digital audio over DVI, is that the bus would be simply 16-bit, as there are 23 digital pins, of which 7 are grounds or clocks. There's a possibility to split the 16-bit mono bus into 2 8-bit stereo bus or even utilize the whole 22 bits to mono or 11 bits per a stereo channel (hey there, Raspberry Pi), with a ground pin left in order not to give you a shock when manipulating. This could be misconnected to a monitor too, but at own risk, since it replaces shielding pins and optionally clocks, so the monitor might melt from electromagnetic interference and rapidly changing clock frequency, as taking those pins into account the standard DVI way.
For this thing to work, it is nedded to write a driver for it, too. I don't feel like the one experienced in x86-64 Assembler, so don't expect anything like this from me as I'm too lazy to learn it. Besides, I don't have time for it.
PWM audio
There could be either analog or digital. The digital would replace the 6 color pins for each monitor to give 2x distinct 5.1 or 7.1 with mixed center channels per connector. The bandwidth is in order of MHz. That is more channels than the Covox idea, but it still requires someone to write a driver for it.
NVidia GPU output possibilities
Current-generation nVidia (sometimes called neVidim by Czechs - iDontSee) graphics cards have DVI-I, DVI-D, HDMI and DP. No D-SUB, because they are digital and nobody uses analog monitors anyway. I've never had an ATI (bought by AMD, but still I call people FanATIcs and NvIdiots), because altough now-AMDs are cheap and silent, they are less reliable, only good for mining Bitcoins to the date. Also even AMD GPUs perform better with Intel CPUs than theirs. Let's introduce some ANSI art of the nVidia cards' outputs now:
│ └────────────────────────────────────────────────────────────────────────┘ │
│ ┌────────────────────────────────────────────────────────────────────────┐ │
│ │ D V I - I │ │
│ │ ┌──────────────────────┐ H D M I D P │ │
│ │ │ ■ ■ ■ ■ ■ ■ ■ ■ ▄ ▄ │ ┌─────────────┐ ┌─────────────┐ │ │
│ │ │ ■ ■ ■ ■ ■ ■ ■ ■ ─┼─ │ └┐▄▄▄▄▄▄▄▄▄▄▄┌┘ │ ▀▀▀▀▀▀▀▀▀▀█ └┐ │ │
│ │ └┐■ ■ ■ ■ ■ ■ ■ ■ ▀ ▀┌┘ └───────────┘ └──────────────┘ │ │
│ │ └────────────────────┘ │ │
│ └────────────────────────────────────────────────────────────────────────┘ │
│ ┌────────────────────────────────────────────────────────────────────────┐ │
│ │ D V I - D ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ │ │
│ │ ┌──────────────────────┐ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ │ │
│ │ │ ■ ■ ■ ■ ■ ■ ■ ■ │ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ │ │
│ │ │ ■ ■ ■ ■ ■ ■ ■ ■ ─── │ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ │ │
│ │ └┐■ ■ ■ ■ ■ ■ ■ ■ ┌┘ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ │ │
│ │ └────────────────────┘ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ │ │
│ └────────────────────────────────────────────────────────────────────────┘ │
│ ┌────────────────────────────────────────────────────────────────────────┐ │
It allows for output of altogether 7 monitors:
4x digital DVI or 4 digital audio channels per 8/11-bit
1x analog DVI or 6 audio channels
1x HDMI with 7.1
1x DP too with 7.1
I don't know if there are some dual-head cables for HDMI or DP, but if yes, then it would be 9 monitors, one of them analog display with 16 (14.2) digital sound channels or 8 digital displays and 22 (22.2 - Super Hi-Vision, some merging required) sound channels (16 + 6 analog). Also, when using that silly Covox idea on DVI-D, the monitor count would drop to 6 and finally there would be distinct 24 channels for the Super Hi-Vision. Though better it would be to have 7 monitors (or 5 if there are no HDMI nor DP dualheads) and the channel number would increase to 28. This is getting too much confusing. Let's summarize it:
Max. monitors: 8 D + 1 A + 16 CH
Max. sound channels: 2 D + 46 CH
Note that both single-link and dual-link DVI suck at 4K (small refresh rate), and even with single-link you can have 60 Hz 2880x1620. I've tested it. So there's no point in running just 1 monitor if you have 2 and a dual-head DVI cable, unless you have that kind of 120 or 240 Hz monitor. But what for if your GPU sucks that hard it cannot into that 120 fps. The motion blur being not acceptable to turn on, your 60 Hz monitor may simulate it when you turn VSync on.
But there's a question: If a human has only 2 ears, is there a point in buying more than 4.2 speakers? Since there are things like EAX and headphones (2.0 is enough, then), absolutely fucking not. If you use wireless sound transition, you will get lot of interference or you will slip on or tie yourself in all the cables to the speakers. Especially valid is this for the Super Hi-Vision, which consists of 24 sound-emitting boxes. And if you enter without slipping or tieing yourself in the cables into a sound sphere with speakers arranged in a platonic body pattern, standing on the subwoofer, you will slip or tie youself in the cables as you exit. To this day, Oculus Rift with noise-eliminating headphones along with a walking disk is the best way to experience the virtual reality.
In the end, similar things can be done with any port. Including HDMI, DP, D-SUB, USB, LPT, COM and even the audio I/O. Nevertheless I wouldn't like to see USB monitors, because USB just sucks as it repaces every known port that has existed in IBM PC ever since 1981. Joystick port, PS/2, LPT, Serial port, all those have been replaced by USB, so I can't connect my old keyboard and printer. I think I should really pick up that now-vintage Pentium III-like computer built by my dad in 2001 for those. It has 900 MHz, 256 MB of RAM, SoundBlaster 16 (nice OPL3 sound), GeForce 100/200 and 2 DVD drives for unauthorized copying, but still for personal purpose. I bet it could run MS-DOS flawlessly. Concerning my birthday, I feel like I've been born about 6 years late, missing all the cool 90's stuff like Second Reality, Doom, Duke Nukem 3D and Quake and, most importantly, the pre-9/11 society, without government spying and annoying restriction about what can be carried on the airplane board. Not even a teddy bear, since it can be used as a weapon. At least a slingshot and stones can be smuggled there. David has stunned Goliath in the fantasy novel called Bible with it, hasn't? There's also the plastic gun called the Liberator, pocket (foldable like a telescope, might be just my silly concept) bow and arrows with stone or carbon tips and, mainly, the power of words.
