HP Visualize c360 PA-RISC Visualize Workstation Universal Serial Bus - Page 9

USB at the Limits

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USB at the Limits Disallowed: • Host-to-host direct cabling. Host-to-host solutions exist, but presently require LAN adaptors, modems or null modems in the cabling path, none of which are transparent extensions of the USB. It is not yet clear if any true bridges or remote-repeaters for USB will appear (the equivalent of LAN bridges, the HP 46082A/B HIL extensions or the HP 37204A HP-IB extender). Strongly Discouraged: • Style A (receptacle) to Style A (plug) passive extension cables. Notwithstanding, they do exist, and can lead to specification violations and unreliable operation. Exception: active cables (5m single-port bus-powered hubs also exist - and they're legal, as long as they aren't used to interconnect hubs). Performance: • Of the theoretical "1.5 MByte/sec." available, in practice, typical sustained throughput is more like 600 KBytes/sec., about 33% lower than asynchronous SCSI (which doesn't provide its theoretical 1.5 MB/s either). The fastest USB device reported to date is a Belkin host-to-host LAN emulator, at 700 KBytes/sec.

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USB at the Limits
Disallowed:
•
Host-to-host direct cabling. Host-to-host solutions exist, but presently require
LAN adaptors, modems or null modems in the cabling path, none of which are
transparent extensions of the USB. It is not yet clear if any true bridges or
remote-repeaters for USB will appear (the equivalent of LAN bridges, the HP
46082A/B HIL extensions or the HP 37204A HP-IB extender).
Strongly Discouraged:
•
Style A (receptacle) to Style A (plug) passive extension cables. Notwithstanding,
they do exist, and can lead to specification violations and unreliable operation.
Exception: active cables (5m single-port bus-powered hubs also exist - and
they’re legal, as long as they aren’t used to interconnect hubs).
Performance:
•
Of the theoretical “1.5 MByte/sec.” available, in practice, typical sustained
throughput is more like 600 KBytes/sec., about 33% lower than asynchronous
SCSI (which doesn’t provide its theoretical 1.5 MB/s either). The fastest USB
device reported to date is a Belkin host-to-host LAN emulator, at 700 KBytes/sec.