The optional plug-in memory modules presented the challenge of how to stuff a maximum number of memory chips into a rugged package with a total volume less than 6 cubic centimeters. The same hybrid subassemblies used for the mainframe memory are employed with beryllium-copper spring contacts for the electrical connection to the mainframe. A one-piece housing that also serves as the card guide allows alignment of the magnetic head without adjustment. Both designs use the same head and magnetic cards with prerecorded timing tracks. The entire mass storage device with 20 discrete components, two hybrid-packaged ICs, magnetic head, and connectors occupies a volume less than 35 cubic centimeters.
Hybrid packaging is necessary to achieve the high functional density.
The circuit board assembly is enclosed by ultrasonically bonded plastic and a stainless-steel cover. The total module volume is 20 cubic centimeters. Summary With the exception of the silk-screened polymeric resistors, none of the design techniques or manufacturing processes are actually new to HP's Portable Computer Division. Instead, the packaging of the HP-71B represents a refinement of the existing technologies. It is the combination of these technologies that makes the HP-71B Computer the most powerful computing device for its size.