I just wrote:

> I'm an engineer old enough to remember exceptionally well those heady days 
> when real men built their own UART modems and BCD displays out of 
flip-flops 
> and nixie tubes.

To add what I just wrote, I just found this bit of text:

"BCD in electronics

"BCD is very common in electronic systems where a numeric value is to be 
displayed, especially in systems consisting solely of digital logic, and not 
containing a microprocessor. By utilising BCD, the manipulation of numerical data 
for display can be greatly simplified by treating each digit as a separate 
single sub-circuit. This matches much more closely the physical reality of display 
hardware - a designer might choose to use a series of separate identical 
7-segment displays to build a metering circuit, for example. If the numeric 
quantity were stored and manipulated as pure binary, interfacing to such a display 
would require complex circuitry. By working throughout with BCD, a much simpler 
overall system results."

    -- http://en.wikipedia.org/wiki/Binary-coded_decimal

I meant to mention exactly this point in my previous posting that BCD is an 
especially inefficient encoding protocol for computers. A BCD-based arithmetic 
processor can be built, but it's much more complicated than a straight integer 
processor-based CPU. 

However, the obverse is even more true if you just want to push numbers 
around in a circuit and display them easily. It requires a fair amount of quite 
complicated circuitry to break an integer-encoded number up and display it as a 
series of digits, and no one in the early days of digital electronics wanted to 
do that, thus the invention of BCD.

Wirt Atmar

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