A system is configured to receive, by one or more servers, a request for a certificate from a user device. In one embodiment, a storage module receives a command to write an upper page of data to memory cells that have already been programmed with a lower page of data. The system can include a cable modem that is configured to recognize SIP-based signaling and traffic on a CMMultimedia Terminal Adapter interface. The drive unit is halted when output detected from the accelerometer exceeds a threshold value for detecting imbalances.