PC vs. Console Install Base
Estimates of the total number of gaming consoles sold to date worldwide can be gathered from a range places including VGChartz, Wikipedia articles, NPD, as well as by those who compile their own data from various sources. Taking all these into consideration, the breakdown of 'next-gen' gaming consoles sold to date around the world is approximately:
Wii: 36 million
XBox 360: 23 million
PlayStation 3: 17 million
That's a total of around 76 million 'next-gen' consoles currently in use globally.
In the other corner, while the total number of PCs can only be approximated, Gartner Inc. places the figure at just over 1 billion PCs currently in use globally.
In both cases, it is recognized that the figures are not completely accurate, but they provide a very clear sense of the relative proportions of the install base of PCs vs. consoles - the ratio is at least 10:1 in favor of PCs. However to truly compare PCs to consoles, we need an indication of what proportion of the PCs would have sufficient graphics power to run the latest games.
Publicly available data from reports by Jon Peddie Research published in articles such as this one and this one provides us with sufficient information to deduce that sales of add-in graphics cards made by Nvidia and ATI total around 20-24 million units per quarter in 2008. Extrapolating the quarterly figure to an annual one equates to roughly 80-100 million graphics cards sold each year. This is the figure for only one year of sales, so it's a very conservative estimate of the base number of PCs with modern graphics cards. Of course some of these cards will be low-end, however since the data pertains to add-in graphics cards sold by Nvidia and ATI in the past year, not onboard graphics solutions such as Intel chipsets, then virtually all of them would be capable of some level of gaming. For example even low-end and two year-old cards can pump out over 30FPS or more in Call of Duty 4. Furthermore, since even cards released two years ago, such as the 8800GTS/GTX, can still game very effectively, it's still a low-end estimate of the total number of 'gaming' PCs in total. To add to the rough calculations above, this study claims that approximately 196 million gaming PCs were shipped between the third quarter of 2005 and the third quarter of 2008. One last piece of valuable information comes from Roy Taylor of Nvidia who recently stated that: "...there is a very large installed base of GeForce gamers. We estimate that we have over 180 million active GeForce users. That's a much bigger installed base than PS3 or Xbox 360."
In summary, looking at the data we wind up with what appear to be roughly equal proportions of machines capable of gaming in the console market vs. the PC gaming market: there are approximately 76 million or more 'next-gen' consoles currently in use around the world; and of the 1 billion PCs globally, we can state with a reasonable degree of confidence that at least 80 million, possibly as many as almost 200 million of them are capable of gaming with the latest titles. If we want to refine the figures down to which machines are capable of 'hardcore' gaming, then we can exclude the Wii from the console stats, bringing us down to 40 million consoles (XBox 360 and PS3); and even if we halve the number of PCs with add-in graphics cards to 40-100 million to account only for medium and high-end graphics cards, we still wind up with at least a 1:1 ratio in terms of the number of gaming consoles vs. the number of gaming PCs. What we can say with a high degree of certainty is that at no point does it look like gaming PCs are being outgunned in terms of sheer volume of console hardware by a 4:1, 5:1 or higher ratio as game sales ratios would suggest.
