Abstract: When a non-volatile memory device is reversibly operationally connected to a computer, the computer executes an application that is stored on the device. The execution causes changes to a non-volatile memory of the computer. After the execution terminates, all such changes are undone, either immediately if the termination was normal or upon rebooting the computer if the termination was abnormal. Before or during the execution, information related to the changes is recorded. The undoing of the changes is based on that information. Examples of such information recorded before the execution include a list of expected changes and a partial or full copy of the computer's non-volatile memory.