Mainframe and supercomputer sales are so soggy that Control Data Corp is to close five plants for one week next month to reduce costs – but it doesn’t expect to have to make any permanent lay offs. The week off without pay will affect some 2,500 employees at three of its plants in the Minneapolis area and ones in Sunnyvale, California and in Kansas City, Missouri. Although supercomputer sales are apparently not sparkling either, work will continue at ETA Systems Corp.