Micropolis Corporation

S Barry McClelland

William J Gervais

Ericson M Dunstan

A 'floppy' disc digital magnetic storage apparatus or subsystem includes a number of interrelated features permitting greatly increased data storage and good access time, while using relatively inexpensive parts. The features contributing to the greatly increased storage capacity include arrangements for providing one hundred tracks per inch, and for holding tolerances so that the position of the magnetic head in the radial direction is maintained within the required value of plus or minus 1.7 thousandths of an inch. Features contributing to the high accuracy of magnetic head positioning, and the resultant high data capacity, include the following: (1) mounting the lead screw which positions the magnetic head with its inner end close to the center of the magnetic disc fixed in position, and with its outer end and the stepping motor secured to it mounted on a leaf spring pushing the motor and the outer end of the lead screw inward toward the inner end of the lead screw: (2) utilizing a simple sheet metal stepper motor having two sets of punched metal teeth which interfit with one another and which are exposed to a central permanently magnetized rotor having north and south poles successively located around its periphery; two coils are provided and each of these coils can be energized in opposite directions, with the four combinations resulting in progressive stepping of the permanent magnetic armature, with every fourth step having a more accurately defined angular position than the three intermediate steps; (3) by a special energization arrangement, the rotor is moved four steps at a time to shift the head from one track to the next, thereby using only the more accurately located angular positions, and reducing the adverse effects of friction on head positioning; (4) the electronic circuitry associated with driving the step motor is configured to offset any time penalty incurred by taking four steps to move one track; (5) the floppy disc is accurately positioned relative to the inner end of the lead screw by forcing the magnetic disc to an interference fit relationship with the driving spindle hub on which it is mounted, and (6) the lead screw is ground to mate with a conical pin secured to the movable head assembly.

High precision floppy disc memory system

A magnetic recording system is provided which encodes four bits of an eight bit 'byte' at a time, and is thus compatible with most general purpose data processing systems which process eight bit bytes. Also, the special magnetic recording code groups which are formed have at least two '0's' between each '1', and always include at least one '1' in each code group, thereby increasing the average frequency of magnetic transitions and reducing the requirements for the phase lock oscillator timing circuit compared to previous methods. In addition, the conversion circuitry for converting from the short data groups to the longer code groups is simplified by the use of a small 'Programmable read Only Memory' or 'PROM' and 'EXCLUSIVE-OR' circuit logic to insure proper code bit groupings of '1's' and '0's' within each code group and at the transitions between code groups. Similar simplifications are accomplished in the implementation of the 'Read' decoding logic; and the shift registers for buffering to the 'Read' and 'Write' Programmable Read-Only Memories, are shared, thereby minimizing the expense of the required serial-to-parallel conversion and returning the PROM parallel output to serial form.

Growing community of inventors

Woodland Hills, CA, United States of America

S Barry McClelland