Abstract—The Cambridge System, comprising a standard IBM System/360 Model 40 and an associative memory, is described from the viewpoint of its implementation using the READ-only control storage of the Model 40. In particular, we discuss the use of the ROS in 1) controlling the flow of data between the CPU and the associative memory registers, and 2) handling translation control, absent page indications, and variable field operand pretesting, when the associative memory is used for page translation in a time-sharing mode of operation. Although the main use of the system is as a computer facility that may be shared simultaneously by up to fifteen users, it may also be used as an ordinary batch processor having a small experimental associative memory among its facilities. The magnitude of the ROS additions and modifications, in terms of numbers of microinstructions, is given.