LCD and Viewfinder
Nikon D3100 has a Fixed Type 3" LCD screen with a resolution of 230k dots. Both the screen size and the screen resolution is up to the standards of this class.
D3100 has a built-in Optical (pentamirror) viewfinder. The viewfinder has a coverage of 95% and a magnification ratio of 0.53x. 95% coverage means that what you see in your viewfinder while shooting will slightly be different from the actual image.
Max Shutter speed
Nikon D3100 can shoot continuously at max speed of 3 fps
and has max shutter speed of 1/4000 sec
D3100 has a built-in flash, and it also has a flash shoe to mount your external flashes too.
Nikon D3100 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 focus points and 1 of these sensors are of Cross-type. Cross-type sensors locks focus faster and more accurate compared to single type sensors. Nikon D3100 also features Face detection AF
where it intelligently detects the faces in the frame and locks the focus automatically.
With Nikon D3100, you can record your videos at a highest resolution of 1920 x 1080 at 24 fps and save in and MPEG-4 formats. Full HD resolution of Nikon D3100 will be adequate in most of the situations. But if you are after the highest resolution videos available, see our list of Top Cameras with 4K (Ultra-HD) Video
D3100 has a built-in Mono microphone and a None speaker.
Nikon D3100 doesn't have any connections for external microphones and headphones. If you need a DSLR camera with external microphone connectivity, consider Pentax K-3 or Pentax K-S2 in a similar price range.
Connectivity and Storage
You can connect D3100 to compatible devices via its HDMI port or USB 2.0 (480 Mbit/sec) port.
Nikon D3100 is powered by battery which provides a shooting life of 550 according to CIPA standards.
Considering that the average battery life of DSLR type cameras is 911 shots, Nikon D3100 has a short battery life for its class so we strongly recommend D3100 owners to buy some extra batteries.
Battery Life Comparison in Entry-Level DSLR Cameras
Pentax K-x with its 1900shots is the model with longest battery life among Entry-Level DSLR cameras. Check the comparison of Nikon D3100 vs Pentax K-x or take a look at Longest Battery Life DSLR cameras list.
Nikon D3100 Features Compared to Main Competitors
You can download Nikon D3100's User Manual here