(Reuters) - Hewlett-Packard Co (HPQ.N) reported flat or lower quarterly revenue in all its operating units on Tuesday, and forecast full-year earnings well below analysts' expectations due to the strong U.S. dollar.

Its shares tumbled 6.6 percent in after-hours trading.

The world's No. 2 PC maker, which has struggled to adapt to the new era of mobile and online computing, is preparing to split into two listed companies later this year, separating its computer and printer businesses from its faster-growing corporate hardware and services operations.

"Revenue was a little short on the top end, the guidance for the second quarter was a little below where the consensus was," said Daniel Morgan, a portfolio manager at Synovus Trust Co.

"Let's wait till October, see if this split is really going to create the shareholder value that (CEO) Meg Whitman is hoping for."

HP said the separation plan will cost about $1.50 per share this fiscal year, which works out as about $2.7 billion overall, although some of those tax-related costs will be recuperable.

Palo Alto-based HP, follows Microsoft Corp (MSFT.O) and International Business Machines Corp (IBM.N) in seeing a negative impact from the strong dollar. HP took about two-thirds of its revenue from outside the United States in the year ended October 2014. The dollar .DXY had risen 14.7 percent in the last six months through Tuesday.

HP said it expected adjusted profit of $3.53 to $3.73 per share for the full year ending October, due to a 30 cents per share hit from currency, well below analysts' average estimate of $3.95.

Revenue dropped 4.7 percent to $26.84 billion in the first quarter ended Jan. 31. Revenue from HP's enterprise services unit declined 11 percent.

The company's net income fell to $1.37 billion, or 73 cents per share, from $1.43 billion, or 74 cents per share, a year earlier.

Excluding items, the company earned 92 cents per share.

Analysts on average had expected a profit of 91 cents per share and revenue of $27.34 billion, according to Thomson Reuters I/B/E/S.

HP shares fell 6.6 percent to $35.95 in after-hours trading. Up to Tuesday's close of $38.49, the stock had risen 9.3 percent since the company announced the split in October.