Why are PCI and AGP cards upside down?

[McCarthy]

I was replying to Leo V's fanless GF4 post and wondering aloud as I often do in replies, decided to ask...

Why are PCI and AGP cards upside down?

The ONLY thing I can see is that it allows -1- more available slot in a mixed PCI/ISA arrangement. If PCI faced upwards like ISA does then they couldn't share a case opening. Say you've got one of those cases with only 5 physical openings you can have, 2 ISA, 3PCI, 1AGP with them flipped, would have to be one fewer ISA or PCI if they faced up. Or if you have 7 like most cases then... I never liked the shared slot idea in the first place because you could never use all of your ISA and PCI slots at the same time.

Is that it? To be able to offer more slots even if you couldn't use them all?

Guess at this point we can't flip them back over and take advantage of heat rising since they'd smash into current cards. And motherboard designers don't expect the hardware up top so they don't leave much clearance meaning even flipping AGP cards where most of the heat is won't even work.

Anyone know for sure?

--Mc

 

[AndyHui]

A number of reasons.

The main reason was to prevent them being inserted into ISA slots, and as you pointed out, allow sharing of an opening. Since ISA is gone now, these reasons are not too relevant.

Heat is a consideration...the majority of the heat produced by these cards is on the side away from the processor.

AGP is really the PCI specification on steroids, so it follows that the cards are designed the same way.

 

[McCarthy]

Thanks Andy. I suppose the sharing thing makes the most sense.

The heat is the reason I don't like the way they are as I'd think the cards would radiate better without affecting the CPU much or at all (after all the heat's still in the case). I keep trying to think in terms of 486's and Pentiums and when I think about this - back then the CPU was in front of the cards and the top area of the board where we find the CPU now was where you'd find the ram and ribbon cable connectors primarily. So the heat would all pool around the cards or get blown around if you had the rare case in those days with a front case fan, but never rise up most efficiently. At least with the few boards I owned in the 486/Pentium days.

Probably just all about sharing since thinking back cards then didn't make that much heat, I'm trying to think if there were any videocards out yet that even had heatsinks then and can't recall any. So without heat to worry about it was an easy way to maximize motherboard features with existing case designs. BTW I did take a quick look at the FAQ first to see if it was there yet before asking

--Mc