Why are AGP/PCI cards upside down?

[NapalmDeath]

Why are AGP/PCI cards upside down with the heat generating IC's facing down.
The PCB and chips are laid out mostly on one side...
The mounting slot and bracket have them face downward.

Doesn't heat rise?

Take a desktop PC, with a flat motherboard.
Now flip it upside down.
Doesn't that have a negative effect on the temps due to the cpu blowing heat down?
Or being in a closed space, it's all about the same?

I know BTX has an air flow design...
yet the upcoming PCI-E cards are still down facing...

Does anyone know the reason ISA to PCI flipped the card orientation??

 

[glugglug]

By putting the chips/metal bracket on the opposite side of the card, the slot is displaced slightly to allow the "shared" PCI/ISA slot.

 

[sao123]

another advantage of having the heatsink on the bottom of the AGP card is this...

on some motherboards....the CPU is directly above the AGP slot. having the heatsink on top could create a situation where they are both "using the same airspace" for cooling. Thus air hot already from the cpu, could not cool the video gpu as well.

 

[ZoNtO]

I think it's just cuz hot air rises, and by mounting the GPU higher it gets hotter, thereby limiting overclocks even further of our beloved video cards........

*SIGH*

 

[JustAnAverageGuy]

So far I think Sao is the closest.

You don't want too many hot objects in such close proximity to each other.

Video cards, northbridges, and CPUs can generate that heat. And not everybody has dual 80mm fans in the back

 

[Confused]

When they introduced PCI, they wanted to be able to use shared PCI/ISA slots. To do that, they had to put the components of a PCI card on the other side. Also, at the time, there were very few tower cases, with the majority being desktop cases. When AGP was introduced, in order to be able to use the same cases, the first PCI slot was "replaced" with an AGP slot, in the same position.

When things moved towards tower cases, the cards then appeared to be "upside down". At the time, heat dissipation was negligible, and no where near the kind of output that cards have today, and therefore they were not concerned about the chips being "on the wrong side".


Confused

 

[NapalmDeath]

I had a feeling it was to share ISA slots with PCI...
That was so many years ago...
ISA is long gone from most motherboards...

With PCI-express, and new BTX boards coming out...
Why didn't they make PCI-express flip the card back around?
Especially with the entire BTX design around a center air channel
and the cpu more towards the front.

I really don't think video card heat dissipation is negligible anymore...

 

[Matthias99]

With PCI-express, and new BTX boards coming out...
Why didn't they make PCI-express flip the card back around?

Uh... I was under the impression that PCI-E video cards did 'face up' (like regular PCI cards -- why would they be different?)

 

[Shalmanese]

Because nVidia want to use a bridged solution for the transition which can save them $2 now but will cause a whole lot of grief 10 years into the future.

 

[Peter]

It's a history thing. PCI cards have the mirrored layout so that PCI/ISA mainboards could have (at least) one "shared" PCI/ISA slot that had both slot types pointing at one slot bracket position, so you could fit either an ISA or a PCI card there.

Like this here example. See how the 3rd slot position from the left takes either a PCI or an ISA card?

Back in the days when this was designed, we were still on AT form factor, and with desktop mainboards. So it wasn't about upright or upside down, it was about components on the right or left side, which doesn't make a difference at all. Besides, power consumption of any kind of card wasn't anywhere near the range where you'd have to care about airflow issues. That didn't become an issue until the 3D rage spawned the NVidia TNT2 chips.

Now, after the departure of ISA slots, Intel's BTX initiative mirrors the entire board so that PCI, AGP and PCI Express cards face the "right" way round again.

 

[NapalmDeath]

They did a musical chairs on the mobo connections, but the cards are still installed upside down.

Take a look at the pic on this link of the BTX layout...
2nd pic down, far right (mid tower)
BTX mobo diagrams

Next take a look at the pic of the ATI PCI express vid card...
Notice where the screw notch is on the bracket.
ATI PCI Express Vid Card

When that card is installed on a new mid tower BTX motherboard, the fan will be blowing down.
PCI express cards will be identical in layout to AGP, PCI cards. UPSIDE DOWN.

After looking at the BTX layout, it's starting to make some sense.
A center air flow from the cpu directly out the back.
Video card heat being blown from the top back down into the center channel.
RAM heat rises up into the center channel.

It looks good on paper, but it sounds like intel came up with the design, and then told the rest of the world to do it.
Sparked by the fact that Prescott is a heater. At Intel's current rate, it won't be long before the WTX (water form factor) standard is issued from intel.

 

[Peter]

No, sorry. What you missed is that the entire BTX case is mirrored. Looking at the front of a tower case, the mainboard will be on the left side, not on the right like now. Hence, the same cards that are upside down in an ATX case will have their component side pointing up in a BTX machine.