Why are PCI cards upside-down?

[DavidX]

It may seem like a silly question but the restriction of having a shared PCI/ISA slot on a motherboard has always irked me. It's either one or the other, and that means a perfectly good ISA or PCI slot goes to waste. (I know ISA is being phased out now anyway but I still have some good ISA cards I like using.) If only they had decided to make PCI cards face the same way round as ISA there would be one extra usable slot.

Any comments?

[socalgal]

I never really thought about that.. and you're right! I wonder why.

[Susan]

Probably so people don't get confused and try to wedge a PCI into an ISA? Hard to do, I know...but I've seen worse http://www.sysopt.com/forum/wink.gif

[Plaster]

They're upside down so you can have one extra ISA slot, or one extra PCI slot.

[Ed_S]

Plaster, you're probably right, and this would make sense if the total usable slots were more, but as it is, a board with 3 isa, 3 pci, 1 agp is really a 6 slot board. If it were 4/4/1, allowing 8 usable, this would be great way to go.

Why do they all make their boards with 6, 7, or less total usable slots when cases accomodate 8 or more? Have written to a few makers w. this question, reply is cost. So what, add another $5 to the selling price!
After all, their product is for builders & customers who want custom-built machines. If cost was the major factor, we'd all buy Packard Bell or HP.

[Ziz]

Ed: True, but look at it this way...when ISA is completely phased out in another couple of years, hopefully we'll start to see boards with 7 PCI/1 AGP...8 slots, all avilable!!! No design factors (aside from maybe the board's entire size) to limit them. Part of the reason there's only one combination slot on any given MB is because there are twice as many traces in that area to accomodate both connectors. When boards become all PCI, they won't have that limitation, hence they'll have the extra space available for the last slot.

As to why the PCI cards are upside down, probaby like Susan said, avoids excessive repair problems due to incompetents who want to put a Voodoo2 card in their old 386...the kind that think "Well I have a computer, it's made for a computer, why can't I use it?" I used to run a Tech Center at Staples and you'd be amazed at the "antique" machines people wanted upgraded. One guy wanted to know why I couldn't put a 13 gig HD into his old 286!! "It doesn't have a hard drive in it now, what's the problem?"

But I'm straying from the subject at hand...

[socalgal]

If all the ISA slots get phased out, then how can we use an ISA vidcard to troubleshoot when we have no video?? ack!

[cobain1crt]

Well, first, although they may phase out the cards, there will always be room for at least 1 ISA, just share it with the 6th PCI, after all, even if they move the PCI all the way down to as low as it will go, you will still be able to fit one shared ISA slot in there! And becides, the last time I checked, both the disket drive and the Parallel (printer) port are hooked up to the ISA part of the chipset, ok, so perhapse you could run this stuff off the PCI, I do not know. But why would you phase out that last ISA, no reason. I wonder if there is a good, cheap case with enough hook ups for 8 cards, my case only has 7 expansion slot spots(all used up by my lovely BH6) Also, I do not know if anyone else has seen this, but all the micro-ATX boards still have 1 ISA, even if they have only a single PCI, and no AGP. Even if they stop making the ISA cards all together, they will most likely keep 1 ISA. Also, here is an idea, e-mail me and tell me what you think...why not have something that plugs into an ISA slot (the one you can't use bacause there is a PCI card there), it plugs into all the spots, puts all the wires into a big line, and omes out with an ISA plug that you hook up a card in, perfect for boards with only 4 PCI and 2 ISA, or for cases with 8 spots to plug stuff in, call it an ISA-extend.

[DavidX]

I imagine Susan is probably right. But is facing the card the other way round really any more likely to foil the dedicated moron than keeping to the ISA orientation? If he/she sees a row of open slots (as opposed to only one slot), he/she is just as likely to try forcing a PCI card into an ISA slot (or vice versa) no matter which way the card faces. I believe (I haven't tried it) that either card would still line up with the apertures on the back of the PC even if in the wrong kind of slot. If it does, then we are back to my original question and none the wiser. (Although I must admit, if there were only one open slot then it would be more of a deterent to the bodger if the card obviously faces the opposite way.)

Cobain
A great idea, but it would have to be for a card which doesn't require external connections (no backplate).

[This message has been edited by DavidX (edited 06-21-99).]

[Susan]

I was kind of kidding when I replied to this post, but not entirely.

But is facing the card the other way round really any more likely to foil the dedicated moron than keeping to the ISA
orientation?

LOL! Probably not! I once replace a MB that the user had tried to install Simms into. He effectively murdered the memory slots on the board and the ram was left unusable. I remarked to him, "What did you do, take a sledgehammer to this thing"? He didn't laugh. Too funny...

[KillerBug]

Well, first, with the PCI facing down and the ISA facing up, you can have 2 together sharing one space, so you can keep ISA around, because why not? As for the moron craming a PCI into an ISA, they would se that there is no faceplate spot there, and not try, unlike the AGP slot.