USB cables

[mutt k]

Trying to get the office better organised, I have found a number of usb cables under the desk that in my wisdom I have not labelled or put back with the equipment they belong to so I now don't know what goes with what. Are usb cables specific to the equipment they come with or does one size fit all, to coin a phrase?

[agent006]

A USB cable is a USB cable, will fit and work in anything (so long as it's got a USB port).

[JonRB]

agent006 said:

A USB cable is a USB cable, will fit and work in anything (so long as it's got a USB port).

Not quite. Cables are rated up to a maximum data transfer rate, so if you use a USB 1.1 cable (12mbps) in a USB 2.0 port (480mbps) you won't get full bandwidth.

Also there are two sizes of plug ('A' and 'B'), so cables are generally described as "A to B", "A to A", etc.

But agent006 is correct in saying that cables are generic and not device-specific.

[sjg]

JonRB said:

Not quite. Cables are rated up to a maximum data transfer rate, so if you use a USB 1.1 cable (12mbps) in a USB 2.0 port (480mbps) you won't get full bandwidth.

There's absolutely no difference between them - it's only 4 wires (power +/- and data +/-) in a shielded cable. Maximum length in the USB spec is 5m and you'd be hard pushed to make a cable so poor it wouldn't work at full speed.

The "high-speed" cables marketed by Belkin and others are just marketing rubbish. 50p USB cables will do the job fine.

[arcturus]

Ok, here is a quote from the USB Specification Source document:

' Testing on existing cables has shown that today’s compliant cables will also support USB 2.0 signaling rates, but there are areas where the parameters on the 1.1 spec need to be extended or clarified to ensure operation at USB 2.0 speeds. '

'Summary of changes: Add to the frequency range of the attenuations table (Table 7-4) to include 200MHz <3.2db and 400MHz < 5.8db.

Specify that the common mode impedance (Zcm) must be 30 ohms +/- 30%

Clarify section 7.1.16 so that one way cable delay is 5.2 ns/m (not 26ns regardless of length).

Tighten cable skew (Sec 7.1.3) to 100ps from 400ps

DC resistance from plug shell to plug shell < .6 ohms'

So as you can see, not all cables are the same.

However it goes on to say:

'About 20 cables, from various vendors and of various lengths, were tested at several different labs. That testing revealed that all cables that were compliant with the current USB specification easily met the proposed new criteria. A few test cables would not meet the new criteria, but those cables were also not compliant with the current specification. So the impact on current USB cables is none if they are USB 1.1 compliant. '

So everyone above is right in a way, but beware non compliant cables. Some sources have stated that only 30% of cables on sale today are USB 1.1 compliant; the rest don't meet that spec.

This info has come from here