A patient monitoring system includes a physiological sensor to sense light after it has passed through tissue of a patient and generate a signal indicative a physiological parameters in response to the sensed light, and a patient monitoring device in communication with the physiological sensor to receive the signal and determine measurements of the physiological parameters from the received signal. The patient monitoring device includes a processor and memory having multiple system images. The patient monitoring device downloads an image upgrade to one system image that the not latest used or tested system image. The patient monitoring device boots the processor from the system image that includes the image upgrade. If the upgraded system image fails, the patient monitoring device boots the processor from another system image of the multiple system images. The patient monitoring device repairs the failed system image.