blocks|key|4200659|text|我认为主要的问题是权力。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4200660|我不会查技术数字和数字，但是如果你把太多的设备放在集线器上，USB端口将无法为所有设备提供足够的电源。|4200661|这里是一个USB集线器，有16个端口+(每面8)，它使用外部电源。|offset|length|4200662|编辑:之前发布的13端口枢纽也有外部电源.|entityMap|0|LINK|mutability|MUTABLE|url|http://www.gizmag.com/brando-super-16-port-usb-hub/9691/^0|0|0|0|I|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|S|8|@]|9|@$F|T|G|U|1|V]]|A|$]]|$1|H|3|I|5|6|7|W|8|@]|9|@]|A|$]]]|J|$K|$5|L|M|N|A|$O|P]]]]

I think the main issue is power.

I'm not going to look up the technical numbers and figures, but if you put too many devices on a hub, The USB port won't be able to supply enough power to all the devices.

<a href="http://www.gizmag.com/brando-super-16-port-usb-hub/9691/" rel="nofollow noreferrer">Here is a USB hub with 16 ports</a> (8 on each side) and it uses an external power source.

edit: the 13 port hub posted earlier also has an external power supply...

blocks|key|4200734|text|7来自规格。USB的理论极限为127个器件，为(2%5E7)-1.它将是128，因为地址有7位，但地址0是保留的。所以我们有127。你有没有注意到49个港口枢纽是7的倍数？此外，还有7层设备的上限，这些条款对此作了解释：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4200735|http://www.totalphase.com/support/kb/10047/|offset|length|4200736|http://www.usblyzer.com/usb-topology.htm|entityMap|0|LINK|mutability|MUTABLE|url|1^0|0|0|17|0|0|0|14|1^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@$D|Q|E|R|1|S]]|A|$]]|$1|F|3|G|5|6|7|T|8|@]|9|@$D|U|E|V|1|W]]|A|$]]]|H|$I|$5|J|K|L|A|$M|C]]|N|$5|J|K|L|A|$M|G]]]]

The 7 comes from the spec. The theoretical limit for USB is 127 devices which is (2^7)-1. It would be 128 because there are 7 bits for the address, but address 0 is reserved. So we have 127. Did you notice how the 49 port hub is a multiple of 7? Also, there is an upper limit of 7 tiers of devices which is explained in these articles:

<a href="http://www.totalphase.com/support/kb/10047/" rel="nofollow noreferrer">http://www.totalphase.com/support/kb/10047/</a>

<a href="http://www.usblyzer.com/usb-topology.htm" rel="nofollow noreferrer">http://www.usblyzer.com/usb-topology.htm</a>

blocks|key|461222|text|这里是一个13端口usb集线器。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|461223|13端口USB集线器|offset|length|entityMap|0|LINK|mutability|MUTABLE|url|http://www.newegg.com/Product/Product.aspx?Item=N82E16817364017^0|0|0|A|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@$D|O|E|P|1|Q]]|A|$]]]|F|$G|$5|H|I|J|A|$K|L]]]]

Here is a 13 port usb hub.

<a href="http://www.newegg.com/Product/Product.aspx?Item=N82E16817364017" rel="nofollow noreferrer">13 port USB hub</a>

blocks|key|461239|text|也许是因为没有人(如99.9999%25)有超过7个端口的用途？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|entityMap^0^^$0|@$1|2|3|4|5|6|7|C|8|@]|9|@]|A|$]]]|B|$]]

Maybe because no one (as in 99.9999%) has a use for more then 7 ports ?

blocks|key|461425|text|有超过7个端口的集线器，我见过集线器通常有10，13个端口。然而，一个USB主机只能有7个设备连接到它。因此，当USB集线器中有比7个端口更多的端口时，内部有几个逻辑集线器。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|461426|因此，我认为，13个港口枢纽在内部被组织为两个枢纽，一个连接到另一个：|461427|(+a)主7端口枢纽，其中1个端口用于辅助枢纽的上行链路，6个自由端口|461428|(+b)二级第二个7个港口枢纽，有7个港口。|461429|总之，它是6%2B7=13端口。|461430|因此，13个端口不相等，6个靠近根集线器，7个端口离根中心更远。当许多集线器被链接在一起时，这一点在某些情况下可能很重要。最近，我在Windows+8中收到一个警告，说我有太多的USB集线器被链接在一起，而离根超过5层的设备会有问题，所以我不得不重新配置它们。|461431|这样做的实际后果是，最好有一个集线器作为所有其他集线器的“源”，而不是依次插入一个集线器，以最小化与根的距离。|461432|最近我尝试了很多USB2.0集线器，最后我用了一个EXSYS+EX-1177。它为外部硬盘驱动器和非电源USB集线器提供了足够的电源.我使用它作为最低级别的集线器，并将其他集线器附加到这个集线器上。|offset|length|entityMap|0|LINK|mutability|MUTABLE|url|http://www.exsys.ch/index.php?main_page=product_info&products_id=210&language=en&zenid=8f72c1dfab539b12e72d987c741468a9^0|0|0|0|0|0|0|0|P|D|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Z|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|10|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|11|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|12|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|13|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|14|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|15|8|@]|9|@$P|16|Q|17|1|18]]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]]]

There are hubs with more then 7 ports, I've seen hubs with 10, 13 ports usually. However, a USB host can have only 7 devices attached to it. Therefore, when there are more ports then 7 in a USB hub, there are several logical hubs inside.

So, I think, the 13 port hub internally is organized as two hubs connected one to the other:

a) primary 7 port hub, of which 1 port is used for uplink for the secondary hub, so has 6 free ports

b) secondary second 7 port hub, with 7 ports.

Together, it is 6+7=13 ports.

Therefore, the 13 ports are not equal, 6 are closer to the root hub, and 7 ports are 1 level further away.
This can be important in some cases when many hubs are daisy chained. Recently I got a warning in Windows 8 saying I have too many USB hubs daisy chained, and devices more then 5 level away from the root will have problems, so I had to reconfigure them.

The practical consequence of this is that it's better to have one hub which acts as a "source" for all other hubs, instead of plugging one hubs sequentially, to minimize the distance from the root.

I have tried many USB 2.0 hubs recently, in the end I have settled with an <a href="http://www.exsys.ch/index.php?main_page=product_info&amp;products_id=210&amp;language=en&amp;zenid=8f72c1dfab539b12e72d987c741468a9" rel="nofollow noreferrer">EXSYS EX-1177</a>. It provides sufficient power for external HDD drives, and non-powered USB hubs. I use it as the lowest level hub, and other hubs are attached to this one.

blocks|key|4200674|text|我怀疑，电力是一个关注，如建议，但也是一个市场的枢纽超过一定规模是不够大，使它值得把它们作为一个共同的项目。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|entityMap^0^^$0|@$1|2|3|4|5|6|7|C|8|@]|9|@]|A|$]]]|B|$]]

I suspect that power is a concern, as suggested, but also that the market for hubs over a certain size isn't big enough to make it worth pushing them as a common item.

Why are usb hubs only available up to 7 ports? Is there something technical that prevents that? I thought USB addressing allowed 127 USB devices to be connected, so that's not it.

EDIT: Thanks for the links for hubs with more ports. There are a lot of them with 7 ports, and I'd never seen one with more. I didn't think 7 was the technical limit, I just wondered why 7 seemed to be so universal.

Here's what I have that plugs into USB:

<ol>
<li>mouse</li>
<li>keyboard</li>
<li>ipod</li>
<li>ipod shuffle</li>
<li>camera</li>
<li>joystick</li>
<li>rudder pedals</li>
<li>throttle quadrant</li>
<li>gps</li>
<li>external HD</li>
<li>memory stick</li>
<li>cell phone</li>
</ol>

Why are usb hubs only available up to 7 ports?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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为什么usb集线器只能使用7个端口？有什么技术上的东西可以阻止吗？我以为USB地址可以连接127个USB设备，所以不是这样的。编辑:感谢更多端口的集线器链接。有很多有7个端口，我从未见过有更多的端口。我不认为7是技术的极限，我只是想知道为什么7看起来如此普遍。下面是我在USB中的插件：鼠标键盘ipodipod洗牌摄像头操纵杆舵踏板节流象限全球定位系统外部HD记忆棒手机

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