What is the System Reserved Partition?

In recent versions of Windows, a special hidden partition exists, the so called System Reserved Partition, to support BitLocker full-drive encryption, the boot configuration database, and the Windows Recovery Environment (RE).

If you’re like me, then you’ve supported users who have gathered just enough Windows power user skills “to be dangerous.” Some of these individuals happen upon the Disk Management console, see the hidden System Reserved partition on their system, and want to “experiment” with it, believing the partition to be unnecessary.

Of course, those of us with a bit more experience know that under most circumstances, we don’t want to mess with this partition. To that point, though, how would you answer the question “What is the purpose of the System Reserved partition, anyway?”

As it happens, the System Reserved partition is an unlettered system drive that is automatically created by Windows 7, Windows 8, Windows Server 2008, and Windows Server 2012 during a clean installation.

In Windows 7 and Windows Server 2008, the partition is 100MB. In Windows 8 and Windows Server 2012, it is 350MB.

The three crucial functions provided are as follows:

  • Boot Configuration Store
  • BitLocker Drive Encryption
  • Windows RE

In this blog post I will first show you how to view the contents of the System Reserved partition. Next we’ll cover each of the three functions of the partition. Finally, I will teach you how to delete this partition, which is sometimes a necessary troubleshooting step when you reinstall Windows. Let’s get to work!

Viewing the System Reserved Partition

Open up the Disk Management console and you’ll see why the System Reserved partition is invisible by default–Windows doesn’t associate a drive letter with the partition. I show you the interface below:

View Systen Reserved Partition

You can view the System Reserved partition from DISKPART or the Disk Management console.

All you have to do to view the contents of the System Reserved partition is to attach a drive letter to the drive. To do this, right-click the partition and select Change Drive Letters and Paths from the shortcut menu.

Because all of the contents of the System Reserved partition are hidden, you’ll need to open the Folder Options dialog box, enable the Show hidden files, folders, and drives option, and disable the Hide protected operating system files (Recommended) property.

As you can see in the screenshot below, you can view the partition once it has a drive letter designation and you’ve revealed hidden system files.

Contents of System Reserved Partition

Once you’ve done your homework, you can view the contents of the System Reserved partition

Here is a quick breakdown of the partition-specific file system contents.

  • Boot: This folder contains the boot configuration database and supporting files
  • Recovery: This folder contains the Windows RE environment that is invoked during the system repair process
  • bootmgr: This file is responsible for locating the active partition and parsing the Boot Configuration Database to load an operating system
  • BOOTNXT: This file’s purpose is largely unknown to…well, just about everybody. I believe that the file has to do with CPU Never eXecute (NX) technology. Let me know in the comments if you read or hear anything different.
  • BOOTSECT.BAK: This file is a backup of the computer’s boot sector, which is responsible for locating bootmgr and completing an OS load

The Boot Configuration Data Store

The Boot Configuration Data (BCD) store was introduced in Windows Vista (blech) and fundamentally changed how Windows computers start up. The BCD is physically a binary file in much the same format as the binary Registry hives. Therefore, we need a special tool to view and manipulate the BCD just like we need a Registry editor to modify the Windows Registry.

To that end, we can use the built-in BCDEdit command-line tool, or a third-party utility like the wonderful EasyBCD from NeoSmart Technologies. I show you this interface in Figure 3.


EasyBCD gives you complete control over the BCD

The bottom line, friends, is that the BCD and its associated files represent how the system detects how many (and which) operating systems are present on fixed disks, where they are, and how they load during each system startup.

BitLocker Drive Encryption

When you consider the purpose of BitLocker Drive Encryption–that is to say, to encrypt your computer’s system volume–the necessity of the System Reserved partition becomes clear immediately.

In short, the BitLocker pre-startup authentication and system integrity verification occur on the System Reserved partition. In Microsoft’s literature, they confusingly refer to the System Reserved partition as the system drive.

Windows RE

Windows Recovery Environment (RE) is a graphical troubleshooting environment that is based upon the Windows Preinstallation Environment (Win PE) that Microsoft uses so heavily with their enterprise deployment tools.

We can access the Windows RE either by pressing F8 during system startup (the timeout value is absurdly low so you might need to perform a system hack to configure a more appropriate value), or by accessing the new Advanced Startup options in Windows 8.

By booting into Windows RE, we have started the system from a non-system disk and are therefore free to perform troubleshooting tasks on the system partition without hazard of file locking and/or user logon issues. In the next screenshot I show you most of the Windows RE interface, where you can see what diagnostic or troubleshooting tasks are possible.

Windows RE interface in Windows 8

Windows RE interface in Windows 8

Of course, we can access the Windows RE by booting a computer from the Windows 8 or Windows Server 2012 media. However, the presence of the RE binaries on the System Reserved partition makes it much more convenient for us to get into RE at any time.

Deleting the System Reserved Partition

In my humble opinion, you should leave the System Reserved partition alone. Besides the obvious stuff (this partition contains the boot files, BitLocker keys, recovery environment, etc.), there is the truth of the matter that the partition is incredibly small–you do not need to recover 350MB of space in all likelihood.


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