Our staff correspondents Jiang Yaping and Luo Hua reported from New York that a federal judge had ordered Wednesday that Microsoft be split into two companies, prescribing the biggest corporate breakup since AT&T and harshly rebuking the software giant for stifling computer-age competition. The monumental ruling by U.S. District Judge Thomas Penfield Jackson was not the last word in a case that could define the limits of companies operating in a high-tech economy. Microsoft has promised to appeal the case, which had been pressed by the Justice Department and 19 states. The case could go to the U.S. Court of Appeals or directly to the Supreme Court. Jackson, who concluded two months ago that Microsoft had violated antitrust law, ordered the company split into one that would oversee the Windows operating system and a second that would handle all other Microsoft software, such as its Word program.