Electronic hot connection of disk drive module to computer peripheral bus

A mass storage subsystem connectable to a host computer and comprising subsystem bus means extending from the host computer to at least one base unit and a removable disk drive cartridge, and a control signal path between the base unit and the removable disk drive cartridge when installed and connected within the base unit;

• the removable disk drive cartridge including:
• housing means,
• at least one storage disk rotatably mounted within the housing means,
• at least one data transducer head within the housing means and positionable by head positioning means at selected concentric data storage tracks defined on a storage surface of the storage disk for writing and reading user data to and from the host computer,
• drive electronics means including said head positioning means and further including bus interface circuit means for directly connecting to said subsystem bus means when the cartridge means is installed and connected within the base unit and cartridge controller means for controlling operations of said bus interface circuit means and said head positioning means and for communicating with said base unit via the control signal path,
• the base unit comprising:
• disk cartridge receiving means for receiving and connecting a said disk drive cartridge means,
• stand-in interface circuit means connected to the subsystem bus means when the disk drive cartridge is not connected and operable within the base unit, for presenting an active and "drive not ready" disk cartridge electrical appearance to the subsystem bus means, and connected to the subsystem bus means in parallel with the bus interface circuit means when the disk drive cartridge is operating within the base unit,
• base unit controller means including cartridge control means for controlling operations of said disk cartridge receiving means for receiving and connecting the disk drive cartridge, and stand-in interface control means for responding to a "drive ready" signal from the cartridge controller means via the control signal path following connection of the disk drive module and for thereupon electronically discontinuing stand-in operation of the stand-in interface circuit means.