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Thread: Any problem using USB 2.0 on systems close to or even below the 266MHz cpu requiremen

  1. #1

    Default Any problem using USB 2.0 on systems close to or even below the 266MHz cpu requiremen

    Lets say I tried using an NT OS like Windows 2000 or XP on a 166MHz Pentium with a USB 2.0 PCI card installed. What would happen? Would the card simply NOT run at it's 480mbps rated speed? Would there be corruption risk during file transfers with USB thumb drives due to the system's cpu being too slow to keep up with the data flow?

    And what if I used USB 2.0 on an actual PII 266 or 300? Any trouble doing that? Any user experience you can report?

  2. #2

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    I use USB on my DOS 7.x tweener with a Cyrix 233 without any problems.
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    I don't see why this would be a problem. USB is packet-oriented, so the packets will come a bit more slowly. Burst transfer will be at USB 2.0 rates, but not sustained transfer rates. But then, it's a rare and precious USB 2.0 peripheral that can keep up a sustained 480mbps transfer.

    That's why, in general, I treat the "transfer speed" claims of USB devices as a bit of snake oil.
    Last edited by Chuck(G); September 16th, 2018 at 10:50 AM.

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    I have a USB 2.0 card with a Pentium II 300. Heavy transfers over USB will max out the CPU leaving the rest of the system unresponsive. Don't try to play games off a USB hard drive.

  5. #5

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    How about USB 2.0 on a PCI based 486? My guess is that it will work, but it won't be able to transfer at the designed theoretical 480mbps because a 486 is too slow? I use USB mostly for thumb drive transfers.

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    Did you read post #3?
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    Quote Originally Posted by computerdude92 View Post
    How about USB 2.0 on a PCI based 486? My guess is that it will work, but it won't be able to transfer at the designed theoretical 480mbps because a 486 is too slow? I use USB mostly for thumb drive transfers.
    I think the problem will be one of voltages preventing a USB 2.0 PCI from working. A 486 with PCI probably has 5 volt slots. USB 2.0 card is much more recent and expects 3.3 volt slots. That is if you are lucky enough to find a 486 where the PCI slots work at all; some were released before cards were available and the slots don't follow the specification.

  8. #8

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    Quote Originally Posted by krebizfan View Post
    I think the problem will be one of voltages preventing a USB 2.0 PCI from working. A 486 with PCI probably has 5 volt slots. USB 2.0 card is much more recent and expects 3.3 volt slots. That is if you are lucky enough to find a 486 where the PCI slots work at all; some were released before cards were available and the slots don't follow the specification.
    I see. But I still don't believe these slow "at or below requirements" CPUs have the muscle to handle USB 2.0 speeds. I just wanted some more posts regarding user experience so I can see proof. Sorry.

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    Quote Originally Posted by krebizfan View Post
    I think the problem will be one of voltages preventing a USB 2.0 PCI from working. A 486 with PCI probably has 5 volt slots. USB 2.0 card is much more recent and expects 3.3 volt slots. That is if you are lucky enough to find a 486 where the PCI slots work at all; some were released before cards were available and the slots don't follow the specification.
    This is not why modern PCI cards don't work in 486 machines. The only way voltage would be an issue is if the USB 2.0 card was only keyed for PCI 3.3v operation, which is extremely unlikely.

    3.3v PCI slots are rarely seen outside the server world and high end workstations, they look like reversed PCI slots with the key in the front, instead of in the back:



    5V PCI (the most common) the slot on the far left. 3.3v PCI (rare) is the second from the left. The two slots on the right are the same story, except the 64 bit variants of the slot.

    Most modern PCI cards are keyed for both slot types and will work in either slot. The thing that prevents many modern PCI cards from working on 486 machines is the same reason why PCI cards don't work in Macs, the firmware on the ROM. While the firmware is x86, modern PCI cards sometimes use Pentium class instructions that cause the card to not work. I have a few Geforce4 MX cards with this issue. You can always dump the ROM and try to replace the offending instructions, but that's a time consuming process that requires low level hardware knowledge.

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