Need to clarify a detail here for the beginners.
Servos called "digital" actually are called that because of the method use to control their movement. Here is one mfg's description. You'll note they mention that both type servos have exactly the same things in them except for the digital's one extra bit. They are either digital or not, btw. If it's sold as a digital, it'll be a digital.
To start with, a ‘digital servo’ is the same as a standard servo, except for a
microprocessor, which analyses the incoming receiver signals and controls
the motor. It is incorrect to believe that digital servos differ drastically in
physical design to standard ones. Digital servos have the same motors,
gears and cases as standard servos and they also, most importantly, have a
Feedback Potentiometer (Pot) just like their standard counterparts.
Where a digital servo differs, is in the way it processes the incoming receiver
information, and in turn controls the initial power to the servomotor, reducing
the deadband, increasing the resolution and generating tremendous holding
power.
(That last paragraph seems to have a bit of advertising BS in it, btw. They will have better resolution, no matter what the price level, but they won't have tremendous holding power unless their advertised torque can do "tremendous". Which highlights the difference in function between the two. Digitals work to hold the position you ask for. They will have more holding power than the non-digital but it won't be tremendous for the smaller sizes. Non-digitals work to get to the position.)