From Sonic Retro
R.O.C.C., or Retro-Orbital Chaos Compressor is a device referred to in the early Sonic the Hedgehog promotional comic. It was created by Dr. Ovi Kintobor, who later became known as the more familiar, Dr. Robotnik. The R.O.C.C. was built to attract and contain the chaotic energies of Mobius into the 6 Chaos Emeralds which, when destroyed, will eradicate evil from the planet.
Also within the R.O.C.C. are Containment Rings. When R.O.C.C. explodes it scatters not only the Chaos Emeralds, but its Containment Rings as well. These are the rings that have been collected in the games since Sonic 1.