Oh man, I hate to be Mr. Pedantic, and posting a week after this was discussed, but I'm coming late to this part of the class and I have issue with this position.  The difference between analog and digital is not the difference between discrete and continuous.

Continuous and discrete are *types of quantities*

* continuous: always another value between two values, ever finer differences possible
* discrete: roughly "countable" (the integers); quantized

Analog and digital are *types of representation*

* analog: quantities are represented by analogous quantities
* digital: quantities are represented by digits, quantity of digits does not directly correlate, the *kind* and *order* of digits is what is important

An unary number system (holding up fingers!) is discrete, but still analog: each raised finger represents one item.  Saving a number in binary on your fingers is discrete and digital, as each finger represents a binary digit, but it does not directly correspond to something counted, and it matters both when it is raised and lowered.

As continuous quantities are necessarily represented via analogs, the two concepts have somewhat merged, but this is an important distinction.

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As an amusing and possibly illustrative aside, while the ENIAC was mostly digital, it had a holdover from mechanical counting machines that made it partially analog.  The adding machine mechanism would have a wheel for each digit, marked so that its position indicates 0 through 9.  To add the two digits on wheel A and B and store the result in B, you would turn A to a lower number (by 1) and simultaneously B to a higher number (by 1) until A becomes zero.  If B turns from 9 to 0, then a mechanism turns the adjacent digit in the number by one to do the carry (which could potentially ripple even further down the number).

The ENIAC was constructed the same way, out of electrical counters.  Each counter is a ring of 10 electrical components, only one of which is active at a time, to represent a digit in some number.  There was a mechanism to add one to the count, switching to the next element in the ring.  A counter could transmit is value by counting down and emitting a pulse each time; like an old rotary phone, digits were transmitted throughout the machine as a series of pulses, and each pulse incremented another counter along by one. The same carry happens when going from element 9 to 0.  These counters were developed for counting faster than the mechanical equivalent, and found use in early electronic computing both for storing and performing addition.

While using base ten requires fewer digits than a purely binary machine, each digit is far more complicated, and transmission is slower.  Several of ENIAC's predecessors and almost all of its successors used base two instead, where counting is reduced entirely to "one or nothing" within each digit, much more easily dealt with as a purely logical operation in the Boolean sense.