USB Hubs: Design Contrasts and Restrictions
USB hubs can be based on bus-powered or self-powered designs as described in sections 7.2.1, 7.2.1.1, and 7.2.2.2 of the USB Specification, Version 1.1, which is available from http://www.usb.org (http://www.usb.org/)
USB hubs can be built that operate in either self-powered or bus-powered mode. Self-powered hubs draw their power from the electrical outlet, while bus-powered hubs draw their power from the USB bus. From the aspect of user experience, hubs operating in self-powered mode have a significant advantage over hubs operating in bus-powered mode for the following reasons:
<TABLE cellSpacing=0 cellPadding=0 border=0><TBODY><TR><TD class=listBullet vAlign=top>•</TD><TD class=listItem>A user can plug any bus-powered USB device into any port on a self-powered hub, and the device will always have enough power to function. The power needed by a bus-powered USB device in order to function can range from a few mA up to a maximum of 500mA.
</TD></TR><TR><TD class=listBullet vAlign=top>•</TD><TD class=listItem>A user can plug a bus-powered USB device into a port on a bus-powered hub, but the device might not have enough power to function. Specifically:
<TABLE cellSpacing=0 cellPadding=0 border=0><TBODY><TR><TD class=listBullet vAlign=top>•</TD><TD class=listItem>Only low-power bus-powered devices are guaranteed to have enough power available from a bus-powered hub port to operate (section 7.2.1 of USB Specification, Version 1.1). Low-power bus-powered devices draw less than 100mA when fully operational. To meet the specification, a bus-powered hub must supply up to 100mA at each port, but must not supply more than 100mA. Typical low-power bus-powered USB devices include mice, keyboards, and other HID devices.
</TD></TR><TR><TD class=listBullet vAlign=top>•</TD><TD class=listItem>A large number of USB devices require between 100mA and 500mA from the hub port when fully operational. These devices will not operate when the user plugs them into a port on a bus-powered hub. Examples of high-power bus-powered devices that will not work with a bus-powered hub include video cameras, page scanners, and floppy disk drives.
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Even if it seems unlikely that a user would use USB for a high-power device, the problem with bus-powered USB hub designs is the user's expectation that any USB device can be plugged into any hub and it will work. This is not true with bus-powered hub designs.
Windows Operating Systems and USB Hub Designs
High-power, bus-powered devices can draw up to 500mA after they are configured by host system software, but must not draw more than 100mA until they are configured (USB Specification, Version 1.1, Section 7.2.1). The device circuitry and self-descriptive information that the host system software requires to enumerate the device are available to the host in this low-power mode.
If the user who is running Microsoft Windows 98 plugs a high-power bus-powered device into a port on a bus-powered hub, the device will not work - and little information will be available to help the user understand why. Windows 98 shows the device as disabled in Device Manager, but does not warn the user with a message, for example, at the time of the hot-plug event.
Windows 98 Second Edition, Windows Me, Windows 2000, and Windows XP give the user more help in such a situation. The device is shown as disabled in Device Manager and the user is also presented with a message that indicates why the device is not operating. However, it is still up to the user to locate an unused port on the PC platform or on a self-powered hub connected to the PC platform. Then the user must disconnect the high-power bus-powered device from the bus-powered hub and reconnect it to a port that will supply enough power.
Using a Pass-through Hub Is Prohibited by USB 1.1
A few USB devices provide what seems to be a port on an embedded hub, but it is nothing more than one end of a USB extender cable. USB extender cables are explicitly prohibited by USB Specification, Version 1.1; see section 6.4.4.
This type of design is often referred to as a "pass through" USB hub, even though it is not a hub at all. Although this type of design can work, the following problems and limitations can occur:
<TABLE cellSpacing=0 cellPadding=0 border=0><TBODY><TR><TD class=listBullet vAlign=top>•</TD><TD class=listItem>A USB device that can be configured by host system software when it is plugged into a port on a specification-compliant hub may not be configured successfully when it is plugged into the end of the USB extender cable that is available in a device including a pass-through USB hub.
</TD></TR><TR><TD class=listBullet vAlign=top>•</TD><TD class=listItem>Extender cables have been shown to be electrically unreliable when participating in data transfers over the USB bus, which is why they are prohibited by USB Specification, Version 1.1.
Note: A device that is configured successfully may not operate reliably.
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There is no way for the operating system to determine whether a pass-through USB hub is employed by a device. To determine if a device uses this unreliable, non-compliant design, see if the device offers only a single USB connector for plugging in a USB device. If there is only a single connector available, then the device could be using a USB extender cable; most true USB hubs offer at least two ports.
To answer the question:
7 port $22.00 to $32.00
http://www.dlink.com/products/?pid=149
4 port $19.00 - $27.00
http://www.dlink.com/products/?sec=0&pid=152
I would also check that your bios is updated and chipset/usb drivers are current.
Dee
Hit any user to continue.