Microsoft posts some interesting information about the uptick in 64-bit versions of Windows 7.

As of June 2010, we see that 46 percent of all PCs worldwide running Windows 7 are running a 64-bit edition of Windows 7. That is, nearly half of all PCs running Windows 7 are running 64-bit. Compared to Windows Vista at 3 and a half years after launch, only 11 percent of PCs running Windows Vista worldwide are running 64-bit. With Windows 7, running a 64-bit OS is becoming the norm.

The reason for the jump in transition to 64-bit PCs can be attributed to a few things. The first is the price of memory has dropped over the last several years making it easier for OEMs to up the amount of memory in the PCs they ship. And most major processors in PCs today are capable of running a 64-bit OS. There are also more and more compatible devices and applications for PCs running 64-bit Windows 7.

OEMs today have fully embraced 64-bit. We have seen many OEMs convert entire consumer lines of PCs to 64-bit only – which can be seen quite a bit today in North America. According to Stephen Baker at NPD, 77% of PCs sold at retail in April 2010 in the U.S. had a 64-bit edition of Windows 7 pre-installed.

I think that last bit is, perhaps, the most interesting. I've seen Windows 7 sales data back to late 2009, and this has consistently shown that most copies of Windows 7 sold with new PCs are, in fact, 64-bit versions. So why is total 64-bit uptick so low, comparatively speaking? My guess is that there are two factors. One, many of the Windows 7 retail copies sold so far have been used to upgrade Windows Vista in-place. And since most of those Vista copies (89 percent) were 32-bit, so were the upgrades. Also, netbooks representing 10-20 percent of total PC sales, and those are almost all selling with 32-bit versions of Windows 7 as well.

Microsoft could have done more to drive 64-bit computing by supporting an in-place 32-bit to 64-bit upgrade path of course.