Here are the spec for both. The one 160 is a bit more powerful at peak power of 3200 watts and depths to 900 feet!!
The 100 has a peak of 2400 and max 200 feet of water.
you can read the 100 here:
http://www.garmin.com/products/ff100/spec.html
And the 160 here:
http://www.garmin.com/products/ff160/spec.html