Other than the obvious aesthetic differences (a compound featuring wheels/cams at the tips and cables in addition to strings) a compound bow most notably features "let-off".

The best way I can describe this is to show you on a graph and roughly describe whats going on...

With a recurve, the draw weight is expressed as #s (pounds) of course, but, as you draw a recurve bow, the further back you draw, the more the weight will increase. So, we use 28" as a standard draw to express the peak weight of a recurve bow..... for example a 45# draw recurve would be hitting 45#s at 28". At just 3-4" it might only be 5#s or so. At 29", it might be up around 48#s. Here is whats is called a draw force curve that will show how the weight goes up as the bow is drawn:





With a compound bow, the peak weight might be 70#s... only compounds have let-off (most do anyway).... that let-off is expressed as a %.... say 80% let off. To keep the math easy, lets say we have a compound that peaks at 100#s with 80% let-off. As you draw the bow back, the force you are pulling will reach 100#s... however, as you approach full draw (also known as the valley) 80% of that weight will be 'let-off' so you will only be holding 20#s at full draw. With a 100# recurve at full draw (lets assume 28") you'd be holding the full 100#s.

Here is a graph showing a roundabout draw force curve for a compound... note at the end (right hand side) the weight drops suddenly to the blue dot.... that blue dot represents full draw.




Here is a link to a website I pulled that last image from that does a pretty fair job explaining compounds in depth.... pretty good read.

http://www.archery-engineering.co.za...ion_guide..htm