The world's two largest hard drive makers, Seagate Technology plc (STX) and Western Digital Corp. (WDC), both reported earnings last week that exceeded analysts expectations and both have posted big gains over the past 12 months and for the year to date.

For the year to date, Western Digital stock is up 15.8% and Seagate stock is up 15%. Over the past 12 months Western Digital shares are up nearly 86% and Seagate is up 77%.

But for last week, Seagate was the clear winner. The company's stock jumped more than 20%, more than double the 9.5% rise in Western Digital shares. What gives?

ALSO READ: American Cities Adding the Most Jobs This Year

Seagate posted $1.38 in adjusted diluted earnings per share (EPS) and $2.9 billion in revenue, compared with consensus estimates from Thomson Reuters that called for $1.08 in earnings per share (EPS) and $2.83 billion in revenue.

Jefferies reiterated a Buy rating for Seagate and raised its price target to $50 from $44. The brokerage firm also noted that the company's strong financial performance was due largely to a focus on high-capacity disk drives across Seagate's product line and less to restructuring savings.

BofA/Merrill Lynch maintains an Underperform rating on the stock and said it is concerned about the sustainability of Seagate's gross margin increase. The analysts also noted that Western Digital benefits from better price points on similar products and thinks that will end up causing Seagate to lose customers to Western Digital.

ALSO READ: States With the Best (and Worst) Schools

Western Digital's revenues of $4.89 billion were higher than its $4.75 billion guidance. It also posted gross margin of 36.7%, ahead of some analysts. Its earnings per share (EPS) of $2.30 were also higher than expected and higher than its guidance. Unit sales of hard drives were slightly lower than some analysts expected on weakness in sales of consumer electronics and notebook computers.

Jefferies has a Buy rating and raised its price target to $96 from $90, and the firm says it expects Western Digital to continue to benefit from both hard drive sales and NAND products.

BofA/Merrill Lynch kept its Neutral rating on the stock but raised its price objective from $77 to $90. Tightness in the market for NAND products will drive prices higher, but the firm's bread-and-butter hard drive sales are expected to be weaker.

ALSO READ: America's Best States to Live In

Western Digital stock closed up 1.3% on Friday at $79.52 in a 52-week range of $34.99 to $81.67. The consensus price target on the stock is $90.62.