The main difference between the MR11 and the MR16 is the size of the bulbs. The size of the MR16 is approximately 2 inches while the size of the MR11 is 1.375 inches.
Additionally, the most common base type for each bulb is different. For the MR16 bulb, the common base is a GU5.3. This means that the MR16 has a 2-pin base with 5.3 millimeters between the pins. The MR11 common base is the GU4. This base is a 2-pin base with 4 millimeters between the pins.
Most MR16 bulbs are compatible with AC or DC. This allows you to use either an alternating current or a direct current, depending on what you have. Most MR16 bulbs will require some type of transformer to convert AC voltage to low-voltage power. Transformers allow for the safe operation of low voltage products on high voltage lines.