The Master Room was the figurative heart of the Dalek City on Skaro. (PROSE: Doctor Who in an Exciting Adventure with the Daleks) Despite being the main operational hub of the city, the Dalek Supreme did not operate from it, residing four levels below in the city's incubation level. (AUDIO: Return to Skaro)
Located on Level 10 of the city, it was the site of the final moments of the Thal-Dalek battle where battle damage disabled the Daleks' power distribution system, disabling them all and aborting their plan to flood more radiation into Skaro's atmosphere. (TV: The Daleks)
When the Master Room was deactivated, emergency autonomic systems placed the Dalek Supreme in a state of suspended animation. Some decades afterwards, the Thal scientist Tryana discovered the Supreme who duped her into believing that it desired peace, having her repair the Master Room. When the First Doctor and his companions returned to the Dalek City, both he and Susan Foreman commented on the Room's now pristine state before both used its instruments to deduce the existence of the incubation level.
After the Supreme had abandoned the ruse and led its revived army on a foiled attack on the Thal City, the Daleks retreated back to their city. From the Master Room, the Supreme addressed the troops before the Thals overloaded the pilfered electricity, destroying the city. (AUDIO: Return to Skaro)