Bubble memory having non-uniformly wound Y drive field coil

A magnetic bubble memory comprising:

• an E-shaped planar frame having a pair of outer legs and a center leg, the frame having X and Y axes;
• a bubble memory chip mounted on the center leg of the frame for propagating magnetic bubbles under the influence of a Z bias magnetic field and a rotating XY magnetic drive field;
• the chip having X and Y axes positioned in alignment with the X and Y axes of the frame;
• the chip further having active components located in a pair of peripheral edge areas spaced apart on the Y axis of the chip requiring a first predetermined magnitude of the drive field to operate, and a plurality of propagation paths located in the medial area of the chip between the peripheral edge areas which require a second predetermined magnitude of the drive field to propagate bubbles along the paths, the second predetermined magnitude being substantially less than the first predetermined magnitude;
• means positioned adjacent the chip for providing the Z bias magnetic field;
• and
• a pair of concentric, mutually orthogonal coils encircling the center leg of the frame and the chip, the coil for providing the Y component of the drive field having a uniformly wound inner layer and at least one outer layer having a gap therein which conforms in size to, and is in registration with, the medial portion of the chip;
• whereby when predetermined signals are applied to the coils to provide the rotating XY field, the first predetermined magnitude of the drive field will be provided in the peripheral edge areas of the chip and the second predetermined magnitude of the drive field will be provided in the medial area of the chip.