By Val Bakh
2.4.1 Drive Letters (part 1)
Disk drives are referred to by using alphabet letters. Drives A and B were commonly used for floppy disk drives, which are now ancient history; virtually no new computers have them anymore. Now drive C is usually the first drive on almost any computer. But what exactly is drive C?
Let’s start with the basic terminology. The device that you install in or connect to your computer is a hard disk drive, or simply a hard disk. It is also often called a physical disk. Before a hard disk can store your data, you must prepare it. You need to initialize the disk, create one or more logical containers, and format them for a specific file system. Although these are all non-trivial steps—each step requires a certain degree of consideration and planning—we’ll skip most of the details and focus on only what is relevant to the main topic. Those logical containers that you create on a disk have many names: partitions, drives, logical drives, volumes—to name a few. Technically, not all of these terms mean exactly the same thing, but most people use them as if they did. Let’s choose one—volume—and stick to it throughout this discussion. So a volume is “the thing” that you assign a drive letter to.
Sometimes, Microsoft has an interesting way of naming things. In Microsoft terminology, a system volume is an active disk volume from which a computer boots. Consequently, the system volume hosts boot files. They usually include some sort of boot manager, which is a program that presents one or more boot menus and loads an operating system. A boot volume is a disk volume that hosts an operating system; it is the volume that you specify during an installation when you are prompted to indicate where you want the operating system to be installed. These two theoretical concepts—a system volume and a boot volume—can both be the same disk volume or can be two separate volumes; generally, it’s up to you how to set up a disk and install an operating system.
In the olden days, installing Windows on a blank computer required substantial preparatory work and could easily turn into a real adventure if you were not properly prepared. Starting with Windows NT, installation CDs became bootable and things got a little easier. Windows Vista came on a bootable DVD with its own mini starter operating system (WinPE) and with almost no questions left for you to answer during a typical installation. Although those Windows versions were generations apart, they had one thing in common: unless you specifically wanted to split your installation into multiple volumes, the operating system, by default, was quite happy to live on a single volume, which combined the functions of a system volume and a boot volume. If you wanted to have multiple instances of Windows on the same computer, you needed to create a separate boot volume for each instance. Each installation knew its boot volume’s drive letter, and usually, each volume’s drive letter remained the same, regardless of which instance of Windows you booted into.
Windows 7 installs easier and faster than even Windows Vista, and on the surface, everything appears to be almost the same. However, there is one important difference: when left alone, Windows 7 will always try to install itself on a boot volume that is separate from the computer’s system volume. And another thing that sets Windows 7 and Windows Vista apart from all earlier versions of Windows is that, whenever possible, they both grab the letter C for the boot volume; that is, of course, unless you know how to trick them.
First, let’s try the classic approach: insert a Windows 7 DVD, and start the computer. It boots into WinPE, and all you have to do is click Install now. If the computer’s hard disk is blank or if it contains a sufficient amount of unallocated space and you select it as the destination for the installation, you end up with two new partitions. One is a 100-MB hidden system volume; it contains a boot configuration data (BCD) store, a boot manager, and a recovery environment (WinRE). The second partition is a regular boot volume—a C drive with a Windows 7 installation.
There are a couple of reasons for this new configuration. First of all, the practice of putting a system volume and a boot volume on separate partitions is tried and true; some of you may have been manually partitioning your computer’s hard disk in a similar manner for ages. This approach is rather convenient, especially in a lab environment, where hosting several installations on the same computer in a multi-boot configuration is not uncommon. Keeping the system volume separate from all of the boot volumes gives you the flexibility to do whatever you need to do with one installation without messing up any other installations and without rendering the entire computer unbootable. Outside the lab, in real life, where people usually have only one installation of Windows per computer, it is somewhat comforting to know that if the only instance of Windows on your computer no longer boots properly, you can press F8 on the keyboard at startup, select Repair Your Computer from the Advanced Boot Options menu, and try to fix the problem by using a few command-line tools that are available in WinRE. Or if nothing else helps, you at least can restore a bare-metal recovery backup that you have been keeping on an external USB hard disk for just that sort of occasion. And one more reason for keeping the system and boot volumes separate is that a separate system volume is required to support BitLocker drive encryption. BitLocker keeps your data on the boot volume confidential, but it needs an unencrypted space to start the computer and unlock the boot volume for you once you have proven that it’s really you.
So far, we’ve covered the basics. The next time, we’ll try a few tricks.