Western Digital Corp.'s earnings showed the value of its SanDisk acquisition and how much it has to lose if a partnership with Toshiba Corp. is disrupted by the desperation sale of the Japanese company's chip unit.

Western Digital has posted results that topped estimates every quarter since completing the $15.8 billion purchase of the memory chipmaker last May and its stock has jumped 31 percent this year.

Contrast that with the single-day 17 percent drop in shares of rival Seagate Technology Inc. after it reporting earnings that still mostly depend on older, less desirable spinning magnetic-disk-based hard drives.