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Windows 7: 100 MB Partition Question


23 Sep 2012   #1

Windows 7 Home Premium 32-Bit - Build 7600 SP1
 
 
100 MB Partition Question

Three years ago when Win 7 came out, I bought a Win 7 Upgrade Disk and did a clean install on my PC. It did not have the 100 MB partition as I remember posting a question and asking if it was a problem that I did not have one and was told things were OK. == Fast forward to a couple months ago, my PC died and I had one built. I used the same Win 7 Disk to do a clean install of Windows. This time I do have a 100 MB partition. It seems almost impossible to have a partition on one install and not on another. Just curious if it is as strange as it seems. Thanks,

My System SpecsSystem Spec
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23 Sep 2012   #2

win 7 ultimate32bit, Win8.1pro wmc 32bit
 
 

My System SpecsSystem Spec
23 Sep 2012   #3
Microsoft MVP

64-bit Windows 8.1 Enterprise
 
 

Hello Jim,

The "System Reserved" partition is not required to create when installing Windows 7, but could be handy to have. More details about it here: What is the Windows Server 2008 R2 / Windows 7 System Reserved Partition? - Welcome to the US SMB&D TS2 Team Blog - Site Home - TechNet Blogs

It basically comes down to how you prepare the HDD before doing a clean install of Windows 7 on whether you will have the 100MB Sytem Reserverd partition or not.


I got more details about it at step 8 here though:

Clean Install Windows 7



Note   Note
  • If you want to have the 100 MB System Reserved partition in addition to the Windows 7 C: partition on a HDD or SSD after installation, then you would need to make sure that all partitions on the drive have been deleted until it is only unallocated space. Next, select the unallocated drive to install Windows 7 on. If there are no partitions on the disk, you will get the 100 MB System Reserved.
  • If you do not want to have the 100 MB System Reserved partition and only the Windows 7 C: partition on a HDD or SSD after installation, then select a formatted partition or drive to install Windows 7 on. If there are any partitions on the disk, you won't get the 100 MB System Reserved.
My System SpecsSystem Spec
.


23 Sep 2012   #4

Windows 7 Home Premium 32-Bit - Build 7600 SP1
 
 

Quote   Quote: Originally Posted by Brink View Post


Note   Note
  • If you want to have the 100 MB System Reserved partition in addition to the Windows 7 C: partition on a HDD or SSD after installation, then you would need to make sure that all partitions on the drive have been deleted until it is only unallocated space. Next, select the unallocated drive to install Windows 7 on. If there are no partitions on the disk, you will get the 100 MB System Reserved.
  • If you do not want to have the 100 MB System Reserved partition and only the Windows 7 C: partition on a HDD or SSD after installation, then select a formatted partition or drive to install Windows 7 on. If there are any partitions on the disk, you won't get the 100 MB System Reserved.
Thanks Brink, Your note solves my little mystery. The first install I had two partitions and the second install only had one partition. That is why I did not get one the first time and did the second time. Thanks,
My System SpecsSystem Spec
23 Sep 2012   #5
Microsoft MVP

64-bit Windows 8.1 Enterprise
 
 

You're welcome Jim. I'm glad it could help.
My System SpecsSystem Spec
23 Sep 2012   #6

Windows 7 Pro x64 (1), Win7 Pro X64 / WinXP Pro x86 on (2)
 
 

Quote   Quote: Originally Posted by bigmck View Post
Thanks Brink, Your note solves my little mystery. The first install I had two partitions and the second install only had one partition. That is why I did not get one the first time and did the second time. Thanks,
The BIOS is configured to have a "#1 hard disk" in the boot sequence. And on that hard drive, there must be one ACTIVE partition. That is where the "boot manager" goes as a result of the Windows installation process. It is this boot manager which begins the sequence of things (including possibly choosing from a menu list of multiple operating systems from which you'd like to select for the actual running environment) that eventually result in getting Windows (or something else) loaded and your desktop for that environment presented.

So... the #1 hard disk in the BIOS boot sequence, and the ACTIVE partition on that hard drive. With a brand new hard drive and nothing else in the environment, in the absence of anything else unusual in the environment or manually overridden by you, that is what the 100MB "system reserved" partition will be created to be... by default. And the new Windows 7 System partition will be a second created partition from the installer.

But...

If you point the Windows 7 installation process to a completely empty hard drive which also is that #1 hard disk in the BIOS boot sequence, then the installer WILL BUILD THAT 100MB "system reserved" partition in which the boot manager files will be placed. And THAT partition will also be set to be the "ACTIVE" partition on that hard drive.

And the installer will then build a SECOND partition, for the actual Windows 7 System itself, which is what becomes your "C-partition" when you boot to that Windows.


On the other hand, if your #1 hard disk in the BIOS boot sequence is some other hard drive (and obviously there must also be an ACTIVE partition on that other hard drive), and you're now pointing the Windows 7 installer to unallocated space on this hard drive as the target for the Windows 7 System partition, then there's no need to build the 100MB "system reserved" partition (which would have held the boot manager files). Instead, the boot manager files MUST BE INSTALLED IN THAT OTHER ALREADY EXISTING ACTIVE PARTITION ON THAT OTHER DRIVE... since that's where the BIOS is going to direct the boot process when you initiate it.

So in this case, you're using the existing ACTIVE partition on the existing #1 hard disk in the boot sequence to hold the Windows 7 boot manager files, but you're putting the newly installed Windows 7 System partition into unallocated space on a second hard drive. Perfectly legal and no problem. But you don't need an additional 100MB "system reserved" partition, because there already is an existing ACTIVE partition on the BIOS's #1 hard disk into which the boot manager files can be placed.

Presumably this means you already have an existing operating Windows system (probably on a partition of that same #1 hard disk, maybe even in the same ACTIVE partition... e.g. like WinXP) so the new Windows 7 installation will create a "Boot Manager Menu" which you will now see at boot time. Your newly installed Windows 7 system (on the other hard drive) will be an entry on that Boot Manager Menu, and will probably have been set to be the default for booting in case you don't respond to select it within 30 seconds.

In other words, the boot process goes to that ACTIVE partition on #1 hard disk and kicks off Boot Manager. If there's a boot manager menu (i.e. two or more operating systems to choose from), that's what you'll next see in order for you to select the true target operating system you want to run. And those operating systems can be on ANY OTHER PARTITION of ANY OTHER HARD DRIVE (including on the same hard drive as the ACTIVE partition of #1 hard disk is located on).


And finally, you don't really have to have more than one hard drive (as my above example described) in order for the 100MB partition to not be required or needed. Simplifying the above example to where you only have (a) one hard drive, so it's of course #1 hard disk in the BIOS boot sequence, and (b) free unallocated space on that hard drive where you want to install the new Windows 7 System partition, and (c) an existing bootable Windows partition on that same drive, e.g. WinXP, whose partition is marked ACTIVE.

By the same principles I described earlier, all that is needed to prevent the need (or automatic creation) of that 100MB "system reserved" partition is to already have an existing ACTIVE partition on the #1 hard disk in the boot sequence. And since that WinXP partition (whose installer sets it ACTIVE, by default, unless you're installing WinXP as a second or subsequent additional Windows... say in an environment which might already have Win98, in which case THAT partition is almost certainly the ACTIVE partition in this multi-Windows environment) on the one-and-only hard drive is already ACTIVE, then the Windows 7 boot manager will install itself into THAT existing partition (since (a) it's ACTIVE, and (b) it's on the #1 hard disk in the BIOS boot sequence).

So into that existing WinXP partition will go the Windows 7 boot manager (on which both the new Windows 7 and the existing WinXP will be placed on the Boot Manager Menu). And into the unallocated space (which you point to when telling the installer where you wanted the new Windows 7 System to go) will be created a new partition which will appear to be C when you boot to it.

And, not to confuse things, but in this multi-boot environment the WinXP partition will actually appear to be a different drive letter than C... when you're booted to Windows 7. And when you're booted to WinXP, its partition will appear to be C (to itself) and the other Windows 7 partition will again be a different drive letter than C. Actually, this is true even in my more complex example above (with multiple hard drives), namely that if you are running multiple bootable versions of Windows with each of them on some partition which is "visible" to the others when they are booted, then each one will see itself as C when booted to itself, and the other partitions will simply have whatever other partition letters get assigned to those other partitions when those other Windows are booted.


So, to summarize:

(1) installing Windows 7 to a brand new hard "empty" drive which is defined as #1 hard disk to the BIOS -> you WILL get two partitions: (a) 100MB system reserved, which will be marked ACTIVE and contain the boot manager files, and (b) second large Windows 7 System partition.

(2) installing Windows 7 as a second or subsequent OS to unallocated space on an existing hard drive which already is #1 hard disk to the BIOS and already has an existing ACTIVE partition (for an already existing Windows, probably): -> Windows 7 installer puts the boot manager files into that existing ACTIVE partition, and installs the new Windows 7 System partition in the unallocated space you pointed to on that same #1 hard disk to the BIOS. The installer will create/add to a Boot Manager Menu to support booting to both Windows versions. There will NOT be a need for a 100MB system reserved partition as the boot manager files went into some other already existing ACTIVE partition on #1 hard disk.

(3) installing Windows 7 as a second or subsequent OS to unallocated space on an existing hard drive which is NOT #1 hard disk to the BIOS (i.e. you have multiple hard drives in your environment) and the #1 hard disk is elsewhere on another drive along with the ACTIVE partition on that other drive which holds the other existing Windows OS and possibly even an already existing Boot Manager and Menu for already existing multi-OS support: -> Windows 7 installer will put its boot manager onto that other ACTIVE partition on that other hard drive, and create or add to the Boot Manager Menu to support booting to both versions of Windows (i.e. both the one on that other hard drive as well as the new Windows 7 being installed on this hard drive). Once again, there will NOT be a need for a 100MB system reserved partition as the boot manager files went into some other already existing ACTIVE partition on #1 hard disk. In this case the new Windows 7 System partition was created in the unallocated space you pointed to on the target hard drive which is OTHER THAN #1 hard disk to the BIOS.
My System SpecsSystem Spec
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