I posted this joke a few weeks ago:

There are 10 kinds of people in the world, those who understand binary and those who don't.

I thought it was hilarious.  I have gotten several emails from people who didn't get it.  Obviously they would be in  the latter group.  One person actually ranted about how I didn't understand binary.  Ok; well I am going to relent, and post an explanation.  An excruciatingly detailed explanation.

Binary is a base-2 number system, consisting only of the digits 0 and 1.  It is just another way of counting that happens to be useful in digital electronics.  The numerical system we are used to is called base-10 or decimal simply because we have 10 fingers.  I suppose if we had only 1 finger we would count in binary, but I digress.

The number zero is represented by 0 in the binary system, and the number one represented by 1, just like in the decimal system.  There are no more numerals available in the binary system, so we add a digit place to represent a larger number, just like in the decimal system when we count from nine to ten.  So, two is represented as 10, three as 11; and again we have to carry to an additional place, so four is represented as 100.

Here is a table for a few binary digits:

Binary	Decimal Equivalent
0	0 (zero)
1	1 (one)
10	2 (two)
11	3 (three)
100	4 (four)
101	5 (five)
110	6 (six)
111	7 (seven)
1000	8 (eight)
1001	9 (nine)
1010	10 (ten)

So read the joke again:

There are 10 kinds of people in the world, those who understand binary and those who don't.

Now leave out the number:

There are ____ kinds of people in the world, those who understand binary and those who don't.

Obviously the blank would be filled with the number two.

So the sentence would be:

There are two kinds of people in the world, those who understand binary and those who don't.

But that's not a funny sentence.  The funny sentence is '10 kinds of people'. '10' is two in binary; that's the joke!  What is even funnier is when people think that you are the one that isn't funny and doesn't get it.  If I've said it once, I've said it 1100100 times; some people are as sharp as marbles.

If you still don't get it, I don't think I can help you.  I give up.  Sorry.