Parallel vs Serial speed

[markw at mohawksoft.com]

> Message: 5
> Date: Wed, 07 Feb 2007 13:27:13 -0500
> From: Tom Metro <blu at vl.com>
> Subject: Re: Parallel vs Serial speed
> To: L-blu <discuss at blu.org>
> Message-ID: <45CA1A01.6060609 at vl.com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>

[SNIP]
> As Mark pointed out:
>
>> The reason why they are slow is that the current needed to drive a
>> fast ~4 volt swing is high based on the inductance of any real length
>> of cable.
>
> ...as you scale up the speed in any interface, you encounter problems
> with the electrical characteristics of the cabling (he meant impedance,
> rather than inductance).

Actually no, pedant point here, however, and inductor has inductance. A
cable (any wire, really) acts like an inductor.

Impedance is is the resistance to the flow of current (mostly used in the
flow of alternating current, but I digress), and while impedance can be a
result of inductance, a cable, being an inductor, has inductance, and a
circuit that incorporates said inductive component may have impedance.

In fact, impedance is not your problem in digital transmission, it is
inductance. An inductor resists the change in current flow. An inductor is
measured in "Henrys" and one henry is one amp per second at one volt.

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