Fourth quarter personal computer numbers for the U.S. market came in from Gartner and IDC Wednesday and for the second quarter in a row, Apple (AAPL) sales grew like gangbusters while the Microsoft (MSFT) Windows PC market actually shrank.

Apple sales in the U.S. were up 20.7%, according to Gartner, while HP (HPQ) was down 21.6%, Dell (DELL) fell 4.5%, Toshiba shrank 2.2% and Asus sagged 11.4%.

Next quarter will be even worse for the broader PC market, according to both Gartner and IDC, as the effects of the floods in Thailand and the hard drive shortage fully kick in.

UPDATE: Several readers have pointed out that when you back Mac sales out of Gartner’s numbers, the rest of the PC industry actually shrank by 8.6%, not the 5.9% drop shown in the chart.