Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of hard-drive makers Western Digital (Nasdaq: WDC) and Seagate Technology (Nasdaq: STX) both rallied today, up by as much as 26% and 16%, respectively, after Western Digital reported strong earnings.

So what: Western Digital's revenue in the fiscal fourth quarter added up to $4.8 billion, with net income of $745 million, or $2.87 per share. On an adjusted basis, the bottom line was $3.35 per share. That last figure handily trounced the analyst expectation of just $2.47 per share in adjusted profit.

Now what: It was a record quarter for Western Digital, and investors are taking it as a positive sign for rival Seagate, which also expects to see record results. Seagate had announced preliminary estimates for its own fiscal fourth quarter, expecting record revenue of $4.5 billion. That company's official results will be released on July 30, but investors already have a good idea of what to expect.

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