Comment 19 for bug 381884

I believe that Macbook Pro 4,1 and newer use newer hardware and thus have a different kernel module (bcm5974). This newer hardware make up the "multitouch" touchpads (i.e. can track something like 11 different independent touches all at once). Older hardware uses the appletouch driver can detect whether there is more than one finger on the touchpad, but do not track position data independently.

Both of these hardware types (and their kernel drivers) feed data to Xorg through the synaptic driver.

Code repos for the newer drivers can be found here:
http://bitmath.org/code/