No, that's not true.

Think about it: with just a switch you can control the motor for forward-off-reverse; a switch is a "digital" device in that it can only ever be in one of two states - on or off.

Thus it must be possible to control a motor - at least to some extent - without a DAC!


See above


Yes!

Try connecting a motor through a simple push-button switch:

If you hold the switch down, the motor runs at full power;

If you keep tapping the switch quickly, the motor will run at something less that full power - depending on just how quickly you can do the tapping.

The principle is exactly the same for controlling the motor from a microcontroller: you get the microcontroller to pulse the power to the motor - if the pulses are more off than on, you get reduced power; if they're more on than off you get more power.

This techniques is known as Pulse-Width Modulation or PWM - it has already been mentioned in this thread.

However, note that this only controls the Power to the motor; if you want to control the motor's Speed, you will need to add Feedback in a control loop...