I found this cable which I thought was a DVI splitter cable but then I noticed the end is slightly different. There's no typical DVI prong. Instead it's all little prongs so it doesn't fit into a typical DVI port. ???
That is a specialized OEM cable that some companies like Dell or HP use with their machines or ATI/NVIDIA use with their cards. They connect to special ports that can output many different types of video signals all via one port. That particular cable outputs two different DVI-D signals for an extended desktop setup.
I had one of those on an old Dell at my office from 2004 I believe, exact same cable.
It wasn't on-board graphics, it was it's own card but for the life of me I can't remember.
I ended up switching it out for a standard graphics card with dual DVI out that had a little more umph to it a few years ago. One of my employees is still using the computer but that graphics card is long gone.