Max Shutter speed
Nikon D90 can shoot continuously at max speed of 4.5 fps
and has max shutter speed of 1/4000 sec
D90 has a built-in flash, and it also has a flash shoe to mount your external flashes too.
Nikon D90 features both Contrast Detection and Phase Detection autofocus (AF) systems which ensures speed and accuracy of focusing in most situations. The AF system has 11 points to choose from. Nikon D90 also features Face detection AF
where it intelligently detects the faces in the frame and locks the focus automatically.
You can download Nikon D90's User Manual here