HP RDX Removable Disk Backup System - Manual (Page 36)

The transfer speed capabilities of a device are often referred to by the USB specification revision in which
the transfer rate was defined. Therefore a USB 2.0 Hub will support high, full and low speed, but a
USB 1.1 hub will only support full and low speed.
The USB specification was developed and is maintained by the USB organization. The USB organization
also conducts a certification program. The USB organization will issue the USB logo to a device,
which has passed a series of tests that verify the device has correctly implemented the USB interface,
as defined by the USB specification. There are many types of USB logos depending on which features
of the USB specification a device supports. A USB 2.0 logo-ed device correctly supports high, full,
and low speed data transfer.
Setting up a USB network
USB is very user friendly. The interface automatically assigns addresses to devices; you simply need to
connect a USB device to a USB port on a system using a USB cable. If you have many USB devices
or need to place a device away from your system, you may place up to a maximum of five USB hubs
between the device and host system and connect them with additional cables.
If you are using a high-speed (USB 2.0) device, make sure that the USB host at the system and all the
hubs between the device and host support high-speed (USB 2.0) transfer.
When using a bulk transfer device, such as an RDX Removable Disk Backup System, do not use other USB
devices that will place restrictions on the USB bandwidth available to the bulk transfer device.
If several USB devices requiring large amounts of the USB network bandwidth are to operate
simultaneously, an additional host must be added to the system. Each device must then be placed into
the separate networks starting at the different hosts. An additional host is typically a new USB HBA,
which plugs into the host system’s PCI slot, creating a new USB host that resides on the network. (Note:
if several USB adapters are placed into a system, demands on the bandwidth of the system bus will
constrain the USB devices’ performance.)
Always use USB logo-ed components in your USB network. This is the best and easiest method to
ensure reliable operation.
USB cables
USB cables are available in a variety of lengths. The maximum cable length is 5 meters. If you need to
place a USB device further than 5 meters from the system, you must use a hub.
Do not use USB cable extenders or couples. These are not recognized or approved by the USB
organization. The USB specification does not allow their use and they are likely to reduce the reliability of
the USB network or cause it not to work completely.
Internal and external USB devices use the same USB cables.
36 USB Configuration Guide