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This is an old revision of this page, as edited by 4.16.250.100 (talk) at 03:13, 26 October 2004. The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Use of SCSI Command Set by USB

Q: I think it would be useful to mention that USB uses the SCSI command set, despite adopting a different physical architecture. This is actually highlighted in the SCSI article. As the current article stands SCSI and USB seem like completely unrelated technologies. Nick 08:50, 20 Aug 2004 (UTC)

A: See USB Mass Storage Rationale of SCSI over USB.

Can someone please explain usb cable types

I know there are at least two and maybe more types of cables for USB - Could someone differentiate them? Is one type of plug/cable for USB 1 and another for USB 2? Or does the cable/plug type not matter? I know they are compatible, does one cable/plug limit the bandwidth?

I have tried to find this on the internet but my searches only turn up vendors trying to sell stuff - it is overwhelming.

Could someone please research this and maybe even put pictures of the USB plug types up on the page?

Oh, and I know that a USB 1 hub would have to be replaced to handle the bandwidth of USB 2, but I do not know if the cables make a difference.

The link to the USB.ORG site includes access to the specs for cables which include pictures (drawings). The A end hooks to the host and the B end hooks to the device. As noted above, in the extension called On-the-go, there is also a hermaphroditic socket which will accept either the A or the B end of the mini-version of the standard cables.

There is no plug/socket change for High speed (480Mpbs) but the cable spec was tightened in the 2.0 version to allow for the higher transfer rates. A 1.1 Spec. hub will work on a 2.0 system but will limit the maximum speed of any down-stream devices to 12Mbps regardless of whether the downstream devices are High-speed capable or not. - richard

USB 2 HS vs. FireWire

I would like to comment on USB2.0 being in direct competition with IEEE 1394. Here are a list of features that makes then resolutely different:

Application domain

  • USB addresses needs for a wide range of devices (mouse, keyboard, modem, hard disk drives, scanner, printer...) that do not exist in IEEE 1394.
  • IEEE 1394 addresses needs of audio-video devices such as videorecorder, digital camera that have no real equivalent on USB.

USB's isochronous mode does apply to streaming devices including videorecorders and audio devices such as speakers, microphones, etc. The High-speed (480Mbps) use of isochronous is directly comparable to use of IEEE 1394/Firewire for these devices - richard

Communication paradigm

  • USB provides host to peripheral communication. A host computer is required in the system.
  • IEEE 1394 provides non-centralized networking. You may build a network with simply a VCR and a TV tuner.

Sylvwild

Yes, the system requres a host - but the USB On-the-go extension allows for the possibility of a unit that is usually used as a device to become a host for the purposes of a point to point conversation as you describe. The initial setup is determined by which end of the cable is plugged in to which unit but is switchable under software control so that the initial device may assume host and vice versa. The USB OTG sockets are hermaphroditic - can accept either the A or B end of the cable. - richard

"Confusingly, the USB Forum has renamed USB 1.1 to USB 2.0 Full Speed; and USB 2.0 to USB 2.0 High Speed."

Huh? The USB Implementers Forum (is that what you meant?) still refers to USB 1.1 and USB 2.0. 1.5 Mbps has always been "low-speed" and 12 Mbps has always been "full-speed"; USB 2.0 added "high-speed".

Can we get a reference for this renaming?

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