HP StoreEver DAT Tape Drives - Manual (Page 50)

USB Configuration Guide 50
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 a tape drive, do not use other USB devices that will
place restrictions on the USB bandwidth available to the bulk transfer device.
If several USB device 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.