As wikipedia says:
"Rock and roll (also known as rock 'n' roll) is a form of music that evolved in the United States in the late 1940s and early 1950s, and quickly spread to the rest of the world.
Classic rock and roll is played with one or two electric guitars (one lead, one rhythm), a string bass or (after the mid-1950s) an electric bass guitar, and a drum kit. In the earliest rock and roll styles of the late 1940s and early 1950s, either the piano or saxophone was often the lead instrument, but these were generally replaced or supplemented by guitar in the mid to late 1950s. The beat is essentially a boogie woogie blues rhythm with an accentuated backbeat, the latter almost always provided by a snare drum.
The massive popularity and eventual worldwide view of rock and roll gave it an unprecedented social impact. Far beyond simply a musical style, rock and roll, as seen in movies and in the new medium of television, influenced lifestyles, fashion, attitudes, and language. It went on to spawn various sub-genres, often without the characteristic backbeat, that are more properly called simply 'rock music'."
Now, this makes me wonder,
how many of these can be called rock n roll bands, if they can, where's Buddy Holly and the Crickets, Johnny Burnette Rock n Roll Trio etc. etc...? I mean not many of them use "one or two electric guitars (one lead, one rhythm), a string bass or (after the mid-1950s) an electric bass guitar, and a drum kit", or play with a "backbeat"? Aren't these more a "derivative form" of rock n roll?
Stylistic origins:
Gospel
Folk music
Blues
Western swing
Cultural origins
United States in the period up to the 1950s
Typical instruments
Electric guitar, string bass or later bass guitar, drums, piano, saxophone
Mainstream popularity
One of the best selling music forms since the 1950s
Derivative forms
Rock, soft rock, pop
Another thing...many of my heroes, Buddy Holly, Eddie Cochran, Johnny Burnette, are dead, but still they talk about and play their music and that after been gone for almost 50! years, isn't that a sign of true greatness I don't know what is....still they're not on the list.
How many of these will be remembered and worshipped in 50 or so years...?
I'm gonna put in a few smilies here so you that I'm NOT criticizing anyone's choice of music etc., but just having a good discussion with a group of friends...

tongue in cheek and all that stuff..
Next round of beers are on me fellas!
