Heheh, it's got nothing to do with heat, dust or BTX. 
Gather round, for I have a story to tell...
Back in the day, motherboards used 8 bit 'ISA' expansion slots, and it was pretty much good. PC's were just used for spreadsheets & word-processing. Nobody considered buying one for gaming (that's what Amiga 500's were for!), and 'multi-media' was a buzz-word which was yet to be born.
Fast forward a few years and graphics use is advancing to the point where an 8 bit bus is no longer enough. People are actually wanting more than 8 colours on the screen at once and resolutions as high as 640 x 480!!!
The PCI bus is created to meet the new bandwidth requirements offering 32 bits data width and bus-mastering to reduce cpu overhead. (VLB is also launched as an alternative at this time but dies off pretty quickly). The thing is though, that the new PCI slots are a very similar size to the old ISA slots, and the industry is worried that people will try and jam their ISA cards into them. Shock horrror!
So the solution they decide upon is to space the PCI slots differently, requiring the card to be made upside down if it's to line up with the slots at the back of the case. A simple solution to help prevent user error.
And that, my friends, is why PCI cards are upside down. Why they chose to keep it that way for AGP & PCIE, I have no idea. Perhaps it made arranging the slots on motherboards easier, or perhaps it just never occured to them to turn things the right way up again!
Gather round, for I have a story to tell...
Back in the day, motherboards used 8 bit 'ISA' expansion slots, and it was pretty much good. PC's were just used for spreadsheets & word-processing. Nobody considered buying one for gaming (that's what Amiga 500's were for!), and 'multi-media' was a buzz-word which was yet to be born.
Fast forward a few years and graphics use is advancing to the point where an 8 bit bus is no longer enough. People are actually wanting more than 8 colours on the screen at once and resolutions as high as 640 x 480!!!
The PCI bus is created to meet the new bandwidth requirements offering 32 bits data width and bus-mastering to reduce cpu overhead. (VLB is also launched as an alternative at this time but dies off pretty quickly). The thing is though, that the new PCI slots are a very similar size to the old ISA slots, and the industry is worried that people will try and jam their ISA cards into them. Shock horrror!
So the solution they decide upon is to space the PCI slots differently, requiring the card to be made upside down if it's to line up with the slots at the back of the case. A simple solution to help prevent user error.And that, my friends, is why PCI cards are upside down. Why they chose to keep it that way for AGP & PCIE, I have no idea. Perhaps it made arranging the slots on motherboards easier, or perhaps it just never occured to them to turn things the right way up again!
