Framingham, Mass.--Worldwide unit sales of personal computers in the second quarter grew by 27% year-over-year, according to preliminary estimates by International Data Corp. The worldwide volume growth was led by the U.S., where shipments rose 35.3% in the second quarter compared with the same period last year. Strong consumer demand coupled with continued falling prices spurred the increase in sales, according to IDC. Compaq Computer Corp. narrowly held its lead as the No. 1 PC vendor in the world over a fast-closing Dell Computer Corp. Worldwide, Compaq holds a 14.6% market share, compared with Dell's 10.8%. In the U.S., Compaq has a 16.6% market share, compared with Dell's 16.3%.