The Virtual Disk API In Windows 7

The VHD Format 
Creating Virtual Disks 
Opening Virtual Disks 
Attaching Virtual Disks 
Querying Virtual Disks 
What's Next 

As I write this, the Windows 7 beta has been available for a few days, and I must say there is a lot to like. As usual, I took a look under the hood to see what is new in the Windows SDK. Windows 7 is very much a minor release as far as the SDK is concerned, and that's a good thing. The fundamentals of writing native C++ applications for Windows 7 have not changed much compared to the way they changed for Windows Vista. Having said that, however, Windows 7 has some completely new features that are sure to interest anyone looking to take advantage of the platform.

One of these features is the Virtual Disk API. Although designed with other formats in mind, the Virtual Disk API in the Windows 7 beta is very much geared toward the Microsoft Virtual Hard Disk (VHD) format popularized by virtualization products from Microsoft such as Hyper-V and Virtual PC.

This really takes me back because I've been involved with virtualization for quite a few years. When I first started working with virtualization technology almost ten years ago, VMware was the clear leader. Then in 2003 Microsoft acquired virtual machine technology from Connectix, and everything changed. All of a sudden there were two big players. It was clear the VHD format that Microsoft acquired from Connectix was well suited to the direction that Microsoft wanted to take with virtualization, namely to turn it into a platform. Whereas the VMware virtual disk formats were proprietary and very convoluted, often changing wildly from one release to the next, the VHD format was from the start straightforward and flexible enough to stand the test of time. In the intervening years, the VHD format has proven itself again and again, having been adopted by other products and technologies within Microsoft and by other software companies, big and small.

For this reason I'm happy to see that Windows 7 supports the VHD format natively. This means that users and administrators can easily create and attach virtual disks as if they were additional physical storage devices, without installing any third-party drivers or tools. You can, for example, use the Disk Management MMC (Microsoft Management Console) snap-in or the DISKPART command-line tool to create and attach virtual disks. You can then partition, format, and use them like any other hard disk on your computer.

Read more: MSDN