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I have a 400 GB hard disk. I want to know if is there any way to divide it in two partition A and B And make them in a way logically isolated from each other! have a Windows 7 in partition A and a Windows XP in partition B. And in each windows ,the OS see only a 200 GB hard disk (I mean in disk management, I see 200 GB as total space)

I mean if is there any way to create a system with one 400 GB hard disk behave exactly like a system with two separate 200 GB hard disks?

FYI : Why? Because if a windows affected by a virus, another one remain safe. For example I'll use internet in Windows-7 Only, and I do my important works in Windows XP!

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Down voter please explain why?! –  TheGoodUser-Amir Aug 25 at 11:29
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Although several answers are valid responses to your question, I'd like to point out that this approach is called Security through obscurity. The United States National Institute of Standards and Technology (NIST) specifically recommends against security through obscurity in more than one document. Quoting from one, "System security should not depend on the secrecy of the implementation or its components.". –  agtoever Aug 25 at 12:04
    
@agtoever Why do you think it is security through obscurity? –  gronostaj Aug 25 at 12:32
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@TheGoodUser-Sp for example, by downloading a filesystem driver, and using it to do low-level access to the disk. There is no need for a program to use the operating system to read a disk: it is only much easier –  pqnet Aug 25 at 13:18
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@TheGoodUser-Sp If you're really concerned about security, buy a second HDD and switch them mechanically (ie. unplug one, plug second one). No technique will make a partition completely inaccessible. Encryption may make it unreadable, but it's always possible to just overwrite it with random bytes to damage data. –  gronostaj Aug 25 at 14:11

4 Answers 4

up vote 3 down vote accepted

If you are satisfied with 200GB volumes then: Yes.

You can partition the disk such that the disk has two 200GB partitions. Add a bootloader which sets one partition to have type NTFS (0x06) and one to another type. Then boot into the 0x06 partition.

The result is that windows will see a 400GB disk with two partitions. One partition will be recognised (the one you are booted from), one will be of type unknown and will be unused.

We used to do this at work with something called XOSL. However this did not work well for us since people tended to share USB pen drives between both OS's and still managed to infect both partitions.

So yes, it can work. But beware of shared mail, shared pen drives, shared SD cards etc etc.

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Which types can I use? As far as I know If I want to have a windows on a partition, I must format it as NTFS? So when I set one partitions in another type (except NTFS) in boatloader doesn't the Windows reside on it corrupt? –  TheGoodUser-Amir Aug 25 at 11:28
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@TheGoodUser-Sp That's the point. On boot you're setting NTFS type on partition you're booting from and unrecognized type on the other one. This way running system won't recognize the other partition. –  gronostaj Aug 25 at 11:43
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@EliadTech in this solution both partitions are NTFS, but only one is marked as NTFS at the time. –  gronostaj Aug 25 at 11:44
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@TheGoodUser-Sp Each partition has its type which is stored in partition table as a single byte. This byte is used to detect what kind of filesystem that partition uses. XOSL could be used to set NTFS type for the partition you're booting and intentionally set incorrect type for the other one. It won't break NTFS itself, but OS won't know it is NTFS. –  gronostaj Aug 25 at 11:57
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I agree that common sense is the best approach. But sadly common sense is not common (especially not before coffee). People do make mistakes. If you only have one computer then a liveCD would be best, next would be two encrypted volumes with no shared boot medium. Third would be VMs (assuming you do not need gaming). All of these are intrusive. I think that GRUB/XOSL and two partitions is a way which works relative well without intruding (and thus without 'skipping that just this once because $some_reason`) which otherwise tends to occur. –  Hennes Aug 25 at 15:17

The only way I can think of is using virtual machines (there are several utilities for that, e.g. free VirtualBox). Each machine gets a share from the HD, CPU and RAM, and this is as safe as it gets.

If that is not an option, than you next best solution would be to encrypt the whole volume using BitLocker, TrueCrypt, etc. Alas, that would only prevent access to the data itself - formatting will still be available. If the malicious user has admin access (or worse, physical access) to your computer, there's isn't much you can do to prevent him from wiping your volume.

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You seem to be saying the same thing Enigman in regards to encryption. But you also mention a Virtual Machine, which is definitely a good idea if it will meet the OP's needs. Even just having the XP partition be virtual would work pretty well. And you are correct that nothing will prevent a complete wipe. –  trlkly Aug 25 at 13:26

Another option would be to set up two Windows installations with one encrypted via bitlocker and the other not (assuming you are happy with this option).

Method 3 in the following link details this process How to multiboot with bitlocker and a non-windows OS You could multiboot 2 Windows OSes this way not just non-Windows.

Personally, I'd opt for a bootable CD/DVD/USB drive running Linux and use that for the Internet but if you want to use Windows the above option would most likely meet your requirements.

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This is the best answer. Although I would recommend having both encrypted, but differently. That's the only way that you can truly isolate the partitions where partition will absolutely not be able to read the other. –  trlkly Aug 25 at 13:23
    
Two encrypted volumes would be best. Though the hard part is to boot those without a shared boot volume. (e.g. use two different pen drives to boot from with the /boot partition on them). Prone to error though, but most secure. –  Hennes Aug 25 at 13:50

The easiest solution I could think of is:

  1. Install Windows 7 on partition 1. It will mount it as C: and the other one as D:.

  2. Install Windows XP on partition 2. It will mount is as C: and the other one as D:.

  3. On both systems open Disk Management and unmount D: partition. On Win7 it will be XP's partition and on XP it will be Win7's partition.

This method won't prevent partition access, but it will make filesystem access much harder. Malware probably won't try to mount additional partitions (it requires elevated privileges, is easily detectable and could be useful for a negligible number of systems).

To unmount a drive in Disk Management, right-click it and choose Change Drive Letter and Paths.... Then select drive letter (in this case D:) and click Remove.

(Note that XP will always name its own partition C: and the rest will be named in physical order, while Win7 will always use physical order. As a consequence, Win7 installed on partition 2 would call it D:. It doesn't really matter for the actual solution, you can choose whatever is more convenient for you.)

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Really nice. Thanks. But how can I unmount a drive? I couldn't find any option to do it in Disk Management –  TheGoodUser-Amir Aug 25 at 11:56
    
@TheGoodUser-Sp I have updated the answer. –  gronostaj Aug 25 at 11:59
    
Thank you dear gronostaj. Can I access an unmounted partition without mounting it again? –  TheGoodUser-Amir Aug 25 at 12:03
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Theoretically speaking you could use some tool to access it, but I'm not aware of any such tool and I doubt someone ever made it, because the point of mounting partitions is to make them accessible. Mounting is system-global, but I guess you could create some kind of workaround by mounting in a directory instead of drive letter and then tinkering with file permissions. –  gronostaj Aug 25 at 12:24
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@pqnet: I think all three of us agree, but we read the question differently. Still, risks and benefits should be noted for a complete answer. –  Hennes Aug 25 at 15:19

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