Control crystal

Large, red crystal embedded within the Dial-home device, directly beneath the center "button."

The control crystal is essentially the central processing unit for the D.H.D., and is required for its operation. If the control crystal is removed the Stargate resets itself, and all memory stored within its systems. Upon reinserting the crystal, any stored memory is flushed out, causing a potential overload.

KEY EPISODES

48 Hours - With the information provided by Adrian Conrad's Goa'uld, Carter removes the main control crystal on a D.H.D. connected to the S.G.C. Stargate, restoring Teal'c's physical form. In the process, the D.H.D. overloads and is destroyed.
Avenger 2.0 - Carter speculates the primary control crystal might have something to do with allowing her and Felger to reset the Avenger virus.
Vengeance - Michael removes the D.H.D. control crystal on the new Taranian homeworld to prevent anyone from leaving the planet.