Abstract: An interface protocol for transmitting variable-sized packets between a host system and a storage device. The protocol supports a plurality of signals for transmitting data between the host system and the storage device. One or more address signals indicate whether the packet includes command, data, or status information. An enable signal indicates when the packets may be transmitted to and from the storage device. Read and write strobe signals are also included to allow the host to request data from and transmit data to the storage device. The protocol includes an extensible command set which includes a function code, one or more interrupt requests, and signals to indicate when the storage device is busy, when the storage device is ready to transfer data, when the storage device is ready to receive bytes from a command packet, when the storage device is ready to receive or transmit a data block, and when the storage device is ready to transmit status bytes.