Shaken investors wiped out nearly a quarter of the value of Apple Computer's shares yesterday, a day after the troubled personal computer maker announced its largest quarterly loss ever and an expensive restructuring plan. Apple shares plummeted $8.25, or 23 percent, closing at $27.50 in Nasdaq trading on volume of almost 19 million shares. Other technology stocks also fell, dragging down the stock markets. [ Page 36. ] Apple's shares now trade at less than half their January price of around $65 each. Some analysts said they expected the stock to remain below $30 for some time. The rout came after Apple on Thursday disclosed the magnitude of its problems, reporting a much bigger quarterly loss than expected and a restructuring that will include the planned layoff of 2,500 employees and consolidation into four business units.