Random Access Memoryram

RAM is memory which the computer can both read from and write to. This is where the computer stores data received front sensors, such as engine RPM or coolant temperature. RAM works like thousands of toggle switches which can be either on or off to represent 0's and 1's. This is how the data is stored in RAM. The switches work like spring loaded switches, therefore they must be held in the on" position electrically. If power is lost, everything stored in RAM is lost.

In most of the computers used on Toyotas, the RAM is divided into two sections. One section receives its power from the ignition switch. This is where data about operating conditions, such as vehicle speed and coolant temperature, is stored. The other section, called Keep Alive Memory, is powered directly by the battery. Information such as diagnostic codes is stored in Keep Alive Memory so that it is retained after the ignition is off. This is why a fuse or battery cable has to be removed to clear diagnostic codes.

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