Re: # of USB ports



JohnO wrote:
"Bob I" <birelan@xxxxxxxxx> wrote in message news:eDaU54dtIHA.524@xxxxxxxxxxxxxxxxxxxxxxx


JohnO wrote:


"JohnO" <johno@!NOOSPAM!heathkit.com> wrote in message news:uiGhRSdtIHA.672@xxxxxxxxxxxxxxxxxxxxxxx


How many USB ports does Win XP/Vista support? Not devices (127) but ports. And, can I add 127 devices to each port within Win XP?



I assume your question is theoretical.

USB supports up to 127 peripheral devices which can be connected with USB hubs to expand the number of connectors. The hubs can be connected more or less in any configuration that you please, but the hub tree must be dendritic* and there can be no more than 15 hubs between the host and any peripheral.

*The A and B connector configuration forces this topology.


Thanks, I found some collaborating info at usbmadesimple.co.uk.

Can I do the 127-thing on *each* of my two physical laptop USB ports, and each of the six ports on the rear of my desktop mobo? Or, is there just one root hub in there being split into several physical ports by an internal hub...using up one of my allowed hubs in the dendritic chain? This kind of thing is hard to google.

And yes, the question is academic, but only partially. I'm writing a tutorial and hands-on lab, the end-user will connect a few devices and we'll use Microsoft's UVCView USB utility to examine the ports and devices and the power they're claiming. The theory says "127", but the practical application is fuzzy and I don't see anyone explaining it.

(reminds me of the commonly quoted file name size limit: 254/255...everyone quoted the MS-provided number, but nobody bothered to try it. I did, and the results were different than what MS implied. Today most of us know that "C:\" and takes away three of that 254...)

-John O



<answering my own question...>

Per wiki: "USB host may have multiple host controllers and each host controller may provide one or more USB ports. Up to 127 devices, including the hub devices, may be connected to a single host controller."

So, my Intel mobo could handle 889 devices.

<wondering how to get the purchase order approved to test this>

-John O

I think you will be having "severe propagation and timing issues" a long time before you get to 127 devices. Much less stacking the wiring and hubs to accomodate nearly 900 USB items. ;-)



You're not helping the cause, Bob, even though you're certainly right. :-) I remember reading about someone building a 127-device system back when USB was new, it was mostly keyboards and mice and hubs, and a stunt at a Comdex or something.

-John O


Quick hunt on google yielded 111 devices at Comdex in 1998

http://www.zisman.ca/Articles/1999/USB.html

.

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