They're the same thing....but the '8' signifies a difference in the language of the sheet music.

I'm not heavy in music theory...but when you read a time signature of '4/4' or '3/4'....the first number represents how many beats per bar and the second number represents how the sheet music translates 'how many beats a whole note gets'.

So in 3/4 time...a whole note gets four beats. In 6/8 time a whole note gets 8 beats. But the same piece of music could have both time signatures.....the only thing that would change is the rules of the sheet music.

By the way....'a whole note' in sheet music is a circle that is not filled in and has no stem. It looks like an O. A half note is an O with a stem that looks like a 'd'. A quater note is a 'd' that is filled in (darken the circle). The stem either points up or down depending on it's place in the ledger. (a 'd' or a 'p') After you assign how many beats a whole note gets....all of the other symbols fall into place. (if a whole note gets 4 beats than a half note gets 2 beats and a quarter note gets 1 beat)

Put simply, if you don't read sheet music...the second number is irrelevant.

The first number is important though cause you need to know it if you want to keep proper time. If the first number is 3 than you count along 1,2,3....1,2,3. If it's 4 you count to 4.....and so on. From that you can extract that there's no difference between counting to 3 or counting to 6. Nor is there a difference between counting to 2 or 4 or 8.