According to the Computer Industry Almanac (March 2005), at the end of 2004 there were 822,15M PCs in use worldwide.
This table describes their geographical distribution. By far, the largest number of PCs in use is in the US (223,81 M, or 27.22% of the total). This is more than three times the number of PCs in Japan, the second largest nation per number of PCs. The number of PCs in use is significantly increasing in China, Brazil, Russia and India.
One out of four PCs is a laptop (24% of total), and close to one out of three in the US.