Bob
Wed May 14 12:30:19 PDT 2008
JohnO wrote:
> "Bob I" <birelan@yahoo.com> wrote in message
> news:eDaU54dtIHA.524@TK2MSFTNGP05.phx.gbl...
>
>>
>>JohnO wrote:
>>
>>
>>>"JohnO" <johno@!NOOSPAM!heathkit.com> wrote in message
>>>news:uiGhRSdtIHA.672@TK2MSFTNGP02.phx.gbl...
>>>
>>>
>>>>>>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