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What: For the second time in as many quarters, shares of Super Micro Computer (SMCI 12.44%) plunged -- this time down 28% as of 12 p.m. EDT Tuesday -- after the network server company announced weaker-than-expected preliminary results. 

So what: More specifically, for its fiscal fourth quarter ended June 30, 2016, Super Micro Computer anticipates quarterly net sales in the range of $520 million to $524 million, significantly below its previous guidance for $580 million to $640 million. Super Micro also expects that will translate to adjusted earnings per diluted share of $0.15 to $0.17 -- again below previous guidance of $0.46 to $0.58 -- including a $0.07-per-share impact due to higher research & development expenses to expand the company's product lines.

Analysts, on average, were modeling adjusted earnings of $0.50 per share on revenue of $581.6 million. 

Now what: Super Micro Computer CEO Charles Liang admitted they're "disappointed" with the performance, elaborating, "Although we have been growing well in mid-size accounts during the past quarters and improving our SAP and global operations, our business has become more dependent on larger customers which has created more volatility in our results."

That statement echos Liang's words in April, when shares of Super Micro Computer plunged after he cited similar large customer weakness that led to disappointing preliminary fiscal Q3 results.

Liang promised more details when the company reports official Q4 results on August 4, 2016, and noted they plan to discuss their "go forward strategy to better utilize [...] capacity to compete more effectively and gain market share." In the meantime, though, given its extended period of weakness, it's no surprise to see shares of Super Micro Computer pulling back hard again today.