According to a source inside Microsoft, over 25 percent of Vista installations in the US at the end of last year were 64-bit. There were several major drivers for the switch to 64-bit, most related to cheap DDR2 DRAM.
Jon DeVaan, Senior Vice-President of the Windows Core Operating System Division, agrees. "From our point of view we believe that we have accomplished the tipping point in terms of 64-bit adoption. Now, this happened to a large degree because memory prices are coming down, and another dynamic that we've seen in the United States is that the retail channel is looking to use RAM upgrades as a way to boost margin. So what that means is that 64-bit machine run rate is increasing rapidly, and that means our ability to support those 64-bit machines fully in the broad ecosystem is a really important thing."
Any PC with 4GB of RAM or more must use a 64-bit installation of Windows in order to address the full amount of RAM. Typically a 32-bit installation would recognize a maximum of 3-3.5GB of RAM.
Instead of purchasing a 32-bit version and then having to change to 64-bit later when they purchase more RAM, many are choosing 64-bit at the start. Over 75 percent of Windows sales are based on OEM installations of new computers.
The majority of Core i7 platforms are also using 64-bit operating systems, due to the triple channel memory setup using more RAM.
Windows 7 is expected to be the last to natively run at 32-bits. The next major Windows revision after it will be 64-bit native, running 32-bit applications through the use of a compatibility layer.
Windows Server 2008 R2, the server version of Windows 7, is already exclusively 64-bit.
With the switch to Windows 7, it would be easiest for PC OEMs to adopt 64-bit exclusively. That would reduce the number of SKUs (Stock Keeping Units) and drivers that would be needed by half, not an insignificant number when you consider that Windows 7 will ship in at least 4 editions. Multiply that by at least 34 localized language versions.
Additionally, the price premium of DDR3 will drop significantly as 50nm production kicks in. DDR3 is the memory of choice for AMD's CPUs using the AM3 socket, as well as Intel's Core i7 and Core i5 (Lynnfield). Due to lower power consumption, DDR3 adoption on laptops is progressing rapidly as well.
"Put more simply, usage of 64-bit Windows Vista is growing much more rapidly than 32-bit. Based on current trends, this growth will accelerate as the retail channel shifts to supplying a rapidly increasing assortment of 64-bit desktops and laptops," said Chris Flores, a Director on the Windows Client Communications Team.
Since 64-bit Vista and Windows 7 can run 32-bit applications, the last remaining hurdle is driver compatibility. Many new devices now have 64-bit device drivers available for Vista, and those should be mostly compatible with Windows 7.
An important tool is the Windows Vista Compatibility Center. Devann thinks that 64-bit support will drive sales: "They can go here and look at 64-bit compatibility, and with the trend that we just saw this is a good place for communicating with your customers about your support for 64-bit, so that they can prefer your product if they have one of these 64-bit systems".
Devann addressed the crowd at WinHEC with the following message, "I urge everyone here to make sure that you have the right 64-bit support, and in general 32-bit software runs fine on 64-bit Windows, but when it comes to drivers, that's where the work is. And with this audience, it's something that we're all acutely aware."