Well, Mark has put in fan control support for Benjamin's fan controller, which has the temperature sensor on board. Since the supply to the fan from the header on the main board is not switched, then the only way to switch a fan in practice is using this board.

Hence: instead of Mark supporting only temp detect from the sensor, the driver could also handle occasional polls of IDE disk temp and he could switch on that too.
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One of the few remaining Mk1 owners... #00015