This question comes up occasionally during the purchasing process, and what is the real differences between machine hardware. This CNC/ DCC comparison is only one of the many differences.
All Mitutoyo automated CMMs use a CNC (Computer Numerical Controlled) machine drive controller, the same type of controller that drives most metalworking machine tools. Most other CMMs are controlled with a method called DCC (Direct Computer Controlled).

CNC:
1. Very precise positioning accuracy.
Since the machine positions using scale feedback, we can position to measurement points accurately to one increment of the linear scale, +/-.00002"
2. Improved Gage R&R
With the high positioning accuracy each measurement, as described above.
3. Greater Tunneling Accuracy
When the CMM is traveling from one 3-D location to another, the scale feedback signal allows the controller to travel virtually in a straight line from point to point. The tunneling accuracy achieved with the CNC controller is rated at +/-.00005".
4. Collision Protection
During machine operation, the machine scales are continuously being read by the machine controller. If the machine would happen to collide with a table obstruction, the controller would recognize that the motors are still drawing power, but the scales are not counting. The machine then acknowledges a collision and stops machine operation.

DCC:
1. Accuracy
Tachometers are not as accurate as linear scales when used for positioning purposes. Variables such as heat in the machine motor will expand the drive shaft which the tachometer is reading. One revolution of a cold shaft will be smaller than that of a warm shaft, adding incremental error in position of each revolution.
2. Tunneling Accuracy
Tunneling accuracy is decreased. This will not allow a large probe to travel through a relatively small location.
3. Gage R&R
The gage r&r will not be as good due to the reduction in positioning accuracy.
4. Collision protection is reduced. This occurs because the machine does not communicate drive position back to the controller. The type of crash detection provided is when the machine reads an overcurrent of electricity because it has discovered an obstruction during measurement.

Again, this is only one difference in machine hardware, others are glass scales and tape scales, temperature compensation, etc...