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The Windows System and Boot Partitions

What exactly are the Windows System and Boot
partitions and how can we tell which is which?


System and Boot.

From WinNT in the mid 1990s to Windows-8 there has been a bootmanager built-in to Windows that can be configured for dual or multibooting. This bootmanager can reside inside Windows on the same partition, or it can be on another partition that may or may not have another install of Windows on it. Up to and including Windows Vista it was the default that the first operating system installed on a computer would have the bootmanager inside of it. Further installs of Windows would not get their own bootmanager but be configured to use the existing bootmanager.

The partition with the bootmanager on it will be called the System partition and the partition with the install of Windows that the bootmanager has booted will be called the Boot partition. If the bootmanager and the booted Windows are on the same partition then that partition will be labeled as both the System and Boot partition. If the bootmanager and Windows are on different partitions then we will have separate System and Boot partitions. It is important to understand that a Boot partition that relies on a System partition will not have its own bootmanager, hence Windows installs on separate Boot partitions are not independently bootable.

It is not always obvious if a machine is employing separate System and Boot partitions. Or you may just be unsure which is the System partition with the bootmanager files on it and which is the Boot partition that a Windows install is running from. The easiest way to check is to open the Windows Disk Management utility where you will see the status of partitions clearly labeled for a range of attributes, including System and Boot.

disk manager screenshot
This shows a hard drive that only has one partition and so the Windows install and the bootmanager must be on the same partition. As you can see it is indeed marked as both System and Boot. (Note: in the Disk Management tool in XP a partition that is both System and Boot will only be labeled as System).


Dism Management screenshot2
Creating a second partition and installing a second Windows will configure the existing bootmanager for dualboot and so when we boot into that second OS we will have separate System and Boot partitions.

Diak Management Screenshot3
No matter how many operating systems or hard drives we add, the System partition stays the same and the booted Windows install will be the Boot partition. In this example the booted operating system is on the third partition of the second hard drive.


Win7 logo

Windows-7 and the System Reserved Partition

From Win-7 it became the preferred configuration to put the bootmanager on a separate small partition that was specifically created and reserved just for the bootmanager. If given free reign the Windows 7 and 8 install routines will automatically create this small System Reserved partition and so even if you only have one operating system on a computer you may still have separate System and Boot partitions. The size of this partition can vary but typically Win7 will make it 100MB, and Windows-8 will make it 350MB in size so that there is room enough to also place the WinRE (windows recovery environment) files there instead of on the same partition as Windows. The System Reserved partition can also be used for configuration data for the WIndows BitLocker drive encryption system, removing the need to create a new partition before BitLocker can be enabled.

Drive letter allocation routines were also changed at this time so that a small System Reserved partition would not be given a letter and the Boot partition would by default be the C: drive.

Subsequent installs of Windows will follow the same pattern as before and all will utilize the existing bootmanager and so when booted will become Boot partitions to the System partition that is the System Reserved partition. Not all Win-7 and 8 machines will necessarily have a system reserved partition as it depends on circumstances at install time if one will be created or not. If not then setup will follow the previous way of doing things and embed the bootmanager, and WinRE, inside the first Windows installed.

Master Boot Record Hard Drives.
All of the above examples are of traditional BIOS based PCs with msdos/MBR partitioned hard drives. On such machines we are only allowed 4 primary partitions, one of which can be made an extended primary partition that can hold multiple logical partitions. The System or System Reserved partition can be any one of the 4 standard primary partitions it is possible to have, which by convention will usually be the first partition on the drive. When there is more than one hard drive it will be the boot drive, the one that the BIOS targets first, that will hold the System partition and so the Windows bootmanager files. A Boot partition can be any primary or logical partition on any internal hard drive, or powered eSATA external drive.

Active Partition.
One primary partition on the boot hard drive in a bios based machine has to be designated as the Active partition before the drive will be bootable. The MBR passes control to the Active partition and so this is the partition that needs to hold the Windows boot files. Hence the Windows System partition is also always the Active partition.


Win8 logo

Windows on UEFI and GPT systems.

The new GUID Partition Table (GPT) when used on the boot hard drive in UEFI enabled computers requires a small system partition on the drive that it calls the EFI System Partition (ESP). When Windows-7 or 8 are installed to a GPT styled hard drive they won't create their own separate Windows System Reserved partition but instead utilize this ESP for the location of the Windows bootmanager files. The ESP therefore becomes a combined System Partition for both the GPT configured hard drive and the Windows operating systems.
disk management screenshot5
Windows still has separate system and boot partitions, just that here the system partition, or System Reserved partition, is combined with the GPT hard drive's own small EFI System Partition.

Notice that there is no Active partition showing on our GPT configured hard drive, because in the absence of an MBR on the drive it is the motherboard’s UEFI firmware that passes control directly to a partition, which always has to be the EFI System Partition, thereby making it the unchangeable equivalent to an active partition.

There is also no provision for or need to create extended and logical partitions on GPT styled hard drives because the 4 primary partition limit has been removed. The Microsoft implementation of the new GUID Partition Table can let us have 128 primary partitions, which should satisfy the needs of most normal humans.


Windows-8 Recovery Partition.

On MBR hard drives Windows-8 creates its larger System Reserved Partition so that there is room to locate WinRE on what will be a combined system and recovery partition. On GPT styled hard drives however the Windows system partition is already combined with the EFI System Partition and so Win-8 will want to create a separate small partition just for WinRE. If allowed to do its own partitioning as install time the Win-8 setup routines will place this new Recovery Partition at the very start of the hard drive, even before the EFI System Partition.
gpt disk partitions
A Win-8 install on a clean GPT drive will produce the partition arrangement shown here. On a drive with existing partitions the recovery partition could be placed elsewhere, or not created at all if there was already a functioning WinRE inside another Windows install - as in fig:5 above.


The GPT drive 'Microsoft System Reserved' partition.

If given free reign at install time both Win-7 and 8 will if possible on GPT configured hard drives create a small 128MB hidden partition that will typically be labeled MSR (microsoft system reserved) partition. Its location on the drive can vary depending on circumstances, but most often it will be between the EFI System Partition and the Windows partition. As far as we know its sole purpose is to be used by the Windows Dynamic Disk volume management system for configuration data. It will be completely invisible and inaccessible to Windows, but it will show up in many third-party partitioning tools such as GParted and Partition Wizard, and also in the Windows command line DiskPart tool. If Dynamic Disks are never going to be used on a machine then this partition can be omitted when manually creating partitions for Windows installations.

If you find you already have an MSR partition between other required partitions then we recommend just leaving it alone as it can’t do any harm. We would advise against resizing an ESP partition to take over the space and we always advise against moving the starting position of existing Windows partitions. We also suggest you don’t just delete it as we have some reservations that it may not be wise to leave empty space between partitions on GPT configured drives.

recovery partition
This disk map view from Partition Wizard shows the same hard drive shown in fig:6 above. As you can see the hidden MSR partition is revealed to be 128MB in size and is unnamed and unformatted and located between the EFI and Windows partitions. Also note that the EFI System Partition is showing as the Active partition, which it always has to be on a GPT boot hard drive. Of important note is that the EFI and Windows partitions are indeed showing a status of System and Boot, but in the opposite order to how Windows labels them - see box......


The Other Way Round.
It is worth noting that Microsoft are alone in the way they refer to separate System and Boot partitions. There is a kind of logic I suppose in calling the partition with the booted operating system the boot partition, but before Microsoft and still in most quarters the operating system is on the system partition and the boot files are on the boot partition.

Leaving out unwanted partitions on GPT drives.

If you don’t want the recovery or hidden MSR partitions then they can be excluded at install time of Windows by manually pre-configuring hard drive partitions in a specific way. If a drive already has an EFI System Partition then all we have to do is ensure that there is no unpartitioned space on the drive for any new partitions to be created. For example if we have the EFI partition first, then the partition for our Windows install, then the rest of the drive as either a data partition or just a temporary partition we have created to fill the space, then the recovery and MSR partitions will be left out of the mix.

Note that in the absence of a dedicated Recovery Partition the WinRE files will be placed on the Windows partition. If you do actually want to have WinRE on the hard drive then it is better for it to have its own partition. If you want to exclude WinRE completely from a hard drive then you can leave unpartitioned space after the Windows partition so that separate recovery and MSR partitions are created, which you can later delete.

Create your own ESP.

If you need to create an EFI System Partition then start by making a standard Fat32 partition. It needs to be aligned to 4K partition alignments and on current Advanced Format hard drives it should be 100MB in size, (for native 4K drives it should be 260MB). The ESP partition can be located anywhere on the drive, but we would put it first. The attributes of the partition then need to be set correctly to define it as ESP and this can be done from the GParted partitioning utility by setting the boot flag.
gparted boot flag
In GParted right-click on your intended EFI System Partition and from the popup menu click on 'Manage Flags' and in the options box that will open put a tick in the checkbox for' boot'.




Spanner iconTech Bench Extra techie stuff for the more advanced.
The command line tool diskpart can be used to create an ESP (EFI System Partition). If the disk is already set as GPT and all partitions are deleted then create partition efi size=100 will make a new and active ESP at the start of the hard drive (for a native 4k drive make size=260). No need to format the new ESP as the Windows install will do that. If you don’t want MSR or Recovery partitions then manually create your other partitions so there is no free space on the drive. If the disk is not already set as GPT then note that using Diskpart and the convert gpt command will also put the hidden MSR partition in place at the very start of the drive, which you can delete if you want before making the ESP.
info iconConfigure UEFI/GPT-Based Hard Drive Partitions with WinPE and DiskPart.


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