A Better Use For The AGP Slot, Decades Later

For a while around a quarter century ago PC motherboards came with a special slot, a little shorter than the PCI slots which ruled the roost back then, and offset from them further into the case. This was the Accelerated Graphics Port, or AGP, a standard created to more quickly serve the 3D graphics cards which were then taking the world by storm. It was everywhere for a few years, then in the mid-2000s it was replaced by PCI Express and faded into obscurity. [Peter] has a Socket 7-based NAS with an AGP slot, and was left wondering whether the unused port could be put to a worthwhile purpose.

AGP is a superset of PCI clocked at 66 MHz, and usually benefiting from having its own exclusive bridge to the processor bus. Thus he reasoned that he could make an AGP to PCI adapter and it might work, as the right connections are all there. A hacked-together version was made by butchering two riser cards, and when a network card worked quite happily he knew he was on to something and made a PCB. There’s a caveat that it only works with 66-MHz capable PCI cards so not everything will work, but if you’re one of the very few people who must be in the market for one, he can do you a PCB.

We’d normally end with a link to a related project here, but we must instead congratulate [Peter]. As far as we can find, this is Hackaday’s first AGP hack, two decades later.

22 thoughts on “A Better Use For The AGP Slot, Decades Later

  1. “We’d normally end with a link to a related project here, but we must instead congratulate [Peter]. As far as we can find, this is Hackaday’s first AGP hack, two decades later.”

    I love this observation – it sounds like a challenge for Hackaday readers future projects.

    Cool project!

  2. My compliments, very cool!

    I wonder how anyone could come up with this idea, and sort of why? Is this retro computing, a personal challenge, a use-what-you-got or.. tech appreciation combined with frugality?

    Genuinely curious, I myself could do something similar (well maybe less successful) but even in the best case the result is likely in the lows on all three metrics; speed, efficiency and ease of use.

    Just for fun?

    1. You ask why, but I ask why not?

      I can’t speak for the author, but for myself this seems like a fun project. Mentally stimulating, challenging and almost certainly not cost effective.

      Personally, I like to keep my mind busy. You always learn a lot doing these sorts of things and come away with a much deeper understanding of how it works that often extends far beyond the specific goal. Whether or not there’s a practical use in the end matters not.

      As for coming up with the idea, I think it’s exactly as the article says. He has an unused AGP port and so naturally the question is what can be done with it? And I imagine many readers here are the type that don’t stop because it is difficult or hasn’t been done before.

      If my life wasn’t so busy, I like to think I’d investigate similar ideas. I have a retro computer with a VLB board and a drawer full of PCI cards — could it be made to work? The initial answer is probably no, but then again maybe nobody has truly looked into it before or taken a non-standard approach.

  3. It’s a little surprising, in retrospect, that (to the best of my knowledge) non-graphics AGP cards were never a thing at the time.

    It would have been a niche, to be sure; but with PCI clock rates being limited by the slowest card, and desktop-class chipsets and motherboards not generally supplying more than one independent PCI bus, it seems like using the AGP port as a not-necessarily-as-good-as-PCI-X-but-doesn’t-require-server/workstation-parts slot for the single most demanding NIC or HBA in an appliance built on desktop-tier x86 parts would have been pretty attractive.

    Selling such devices standalone would have been a little dicey, given the odds that a fair few motherboards make assumptions at the firmware level, and probably some OSes at the driver level, that the AGP slot will be a GPU or empty; but if it’s just an option card for your product that’s less of an issue.

      1. Those arent even standard usb. Those are powered usb for use mainly in cash registers for running receipt printers, payment terminals, check frankers, pole signs, scales, etc. They put out 12V or 24V (port color matters), and up to 30 or 40 watts of power

        1. Whoops- up to 144 watts of power. The implementation allows a choice of three different voltages, providing power at 5 V (30 W), 12 V (72 W), 24 V (144 W) as well as a custom voltage. Some implementations provide 19 V or 25 V. The connectors are able to operate at up to 6 A (3 A per pin) peak, but according to the specification, hosts are required to provide a minimum sustainable rms current of 1.5 A at 5 V (7.5 W) or 12 V (18 W), or 2.3 A at 24 V (55.2 W), only.

          1. Seen these before red/orange 120v blue 30v,on a motherboard . They have a double box on the receptacle but standard usb fits in the bottom one.

    1. Ive always wondered why nothing other that video cards used that slot. I work with computer recycling and find a lot of weird cards with few produced, and the only thing close to not being a gpu, was a dual purpose video card that also did capturing

  4. For using an old computer as a server putting a SATA controller or Ethernet card on the AGP slot would be great with several caveats. The biggest one is as AGP went through multiple iterations signal voltages dropped from 5/3.3V to 1.5V to 0.8V; later AGP ports would not want a PCI card in them. Some socket 7 boards had a chip that tacked on AGP, there may not be a performance benefit on those boards. Some low end chipsets had a garbage implementation of AGP (the Alladin line comes to mind).

    A gigabit pci-x card in a PCI to AGP adapter running 32bits @ 66MHz would be able to go at or close to full duplex. A SATA pci-x card would be able to saturate a SATA I link and get close to SATA II speeds on a single port. For chipsets that provide separate paths for PCI, AGP, and PATA would let a server not have storage, swap, and network fighting for the bus. That would squeeze a little more performance out of a specter/meltdown proof CPU.

    1. I’m glad you got the point of this adapter. The limited compatibility due to the different voltage levels used by AGP is a big downside, but I’m already working on some projects that’ll address this problem.

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