Abstract: A data communication system wherein four independent frequencies provide for transmissions between a communication controller and at least one node including a first node. The four independent frequencies include: an aligning signal sent on a first frequency, a request signal in a slot allocated to a first node for transmitting reserved request sent on a second frequency, a authorization signal sent on a third frequency and data packets sent over a fourth frequency. In addition, data packets sent over the data communication system can include information related to a count value and termination indication information for determining whether the message has been completely received.

Abstract: In order to increase the performance and reliability of devices including rotatable storage media, individual characteristics of device elements or heads can be determined and used to set performance criteria. The off-track capability and track mis-registration of an element or head can be determined and used to set individualized thresholds for elements or heads of devices including rotatable storage media.