Abstract: An interface circuit replaces a selected IDE command received from a host computer with an invalid command and routes the invalid command to a data storage device. In this manner, the interface circuit provides convenient, cost-effective technique for preventing a selected IDE command sent by the host computer from reaching the data storage device. Moreover, by replacing the selected command with an invalid command, rather than merely blocking the selected command, the data storage device can respond with an error message rather than leaving the data storage device and the IDE bus in a non-deterministic state that might require user intervention. The interface circuit is particularly well-suited for preventing a host computer from writing to an IDE hard disk drive in a gaming machine.