MIKE ROSS wrote in a message to Greg Mayman:

 MR> There is one other parallel, that of ECL logic. It is used in
 MR> frequency counters for the prescaler divider and up into the
 MR> gigahertz range too. ECL uses small differential signals to drive
 MR> the logic functions. The interesting bit is that ECL doesn't use
 MR> saturated switches like TTL. 

Yeah,  it uses differential _currents_.  I never did run across much of
anything with regard to that stuff,  excepting those entries in my more
general catalogs and such,  things like the "Motorola Master Selection
Guide".

And there was "HTL" (a higher-voltage logic,  usually run off a
12 volt supply,  and intended for industrial uses apparently) and DTL, 
both of which seem to come and go fairly quick.  And RTL,  which I always
thought was rather interesting stuff,  and for which a few projects
appeared in the hobby magazines.

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