PC shipments decreased about 14% in the first three months of 2013 compared with a year ago, IDC says. That's the biggest drop in almost 20 years, analysts said. IDC says mobile-computing devices continue to gain popularity and sales, contributing to the PC slide. Weak demand for Windows 8 may also be a culprit. "Microsoft will have to make some very tough decisions moving forward if it wants to help reinvigorate the PC market," IDC's Bob O'Donnell said in a statement.