On Wed, 13 Aug 2003 at 11:02:53, Jerome Grimbert wrote: (ref: <[EMAIL PROTECTED]>)
Norman Dunbar makes some magical things to make me read } Marcel wrote : } } >> I'm far from being a hardware genius, but I guess that as the end of } >> the cable is not terminated when there's no drive attached you get } >> noise on the data lines due to reflections at the unused cable end. } } Neither am I (as you probably all know) but how on earth can 'electricity' } get reflections from the end of a cable ? } I mean, it should just leak out the cut end shouldn't it ? :o)
No, it never leak! The signal propagates along the line, and when it reach the end of the line, it partially reflect (just like waves do on harbour) and then propagate back, crossing the new incoming signal... The bad thing is that the device in the middle of the cable is only able to detect the level of the wave, not its component part, neither which component cames from which direction.
If you thing of electricity like of water, you must remember that waves DO NOT
move the water horizontally, but mostly VERTICALLY. (unless
there is a continuous current, but this is not the case with a signal transmission line).
Water is a very good analogy for explaining simple electrical circuits. Very good for youngsters.
Battery == pump
Capacitor == expansion vessel. This can be a chamber with spring load diaphragm, or a vertical tube. The National grid use just this to pump water into reservoirs for emergencies.
Voltage == pressure
Amperage == average rate of flow
Resistance == restriction in pipe (well not quite - any better analogy?)
Switch == in line tap
Socket == tap
Hose == Cable insulator
Inductance doesn't quite fit in though does it? .... but that is not simple electricity (8-)#
Unfortunately, when the direction of DC current was decided, they didn't know about electrons (8-(#
> <snip>
... but I find very few people think properly about termination.To make things more complex, even the connection of the wire in the middle for the intermediate device will generate reflection, but it usually perturbate only the generator... hence one reason that IDE is restricted to Two devices per cable, whereas SCSI get a more subtle requirement and copt with reflexion a little better. (at price, of course!)
Unfortunately a simple scsi system will work (up to a point) with wrong termination (much like IDE).
.... and SATA (serial IDE) is already here giving the possibility of chaining IDE devices.
I assume, Nasta, it is in no way compatible with qubide.
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