Irvine-based disk drive maker Western Digital Corp. on Wednesday reported December quarter earnings and revenue that beat Wall Street expectations.

The company posted sales of $4 billion, up 5.2% from a year earlier.

Analysts on average had forecast sales of $3.85 billion.

Adjusted profits hit $532 million, up 3.7% from a year ago and beating analyst estimates of $491.5 million.

The company said it sold 63.1 million hard drive units, compared to 59.2 million units shipped a year ago.

Hard drives use spinning disks to store data, unlike the company’s growing line of solid-state drives, which use chips.

Western Digital’s disk drives go into computers, external storage devices, corporate networks and consumer electronics, such as DVR players.

The company's shares are relatively flat in extended trading with a market value of $20.8 billion.

Cupertino rival Seagate Technology Inc. is scheduled to report December financial results after the close of trading Jan. 27.