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I was reading about NTFS and the use of the driver ntfs.sys and I was wondering how could the NTFS driver be loaded if it's on an NTFS partition.
I couldn't find any answer for this online and I was curious to know how it works.

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ntfs.sys is the NTFS driver for the Windows operating system. However, Windows does not start itself. It relies on the Windows Boot Manager. Windows Boot Manager and winload have built-in NTFS support. It is likely not as full-featured as ntfs.sys.

Windows Boot Manager (or rather winload) is responsible for loading all early drivers. These also include disk controller drivers (AHCI, NVMe, …)—otherwise, Windows could not continue booting.

This situation is somewhat comparable with Linux: GRUB, a popular Linux boot manager, includes support for many filesystems, including the ext family (ext2/3/4).

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    I guess, "Windows Boot Manager and winload will have read-only capability/access with no knowledge of users, etc" to load & enable booting, while "Driver ntfs.sys will have write-capability, knowledge of users and full-access" to enable regular usage.
    – Prem
    Jan 16 at 10:32
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    @Prem - This sounds right.
    – Stilez
    Jan 16 at 14:13
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    And as a historical curiosity: in 1990s most bootloaders (such as lilo, but possibly Windows also) didn't understand filesystems at all, but the operating system installation stored the sector address of the necessary files inside the bootloader itself.
    – jpa
    Jan 16 at 19:16
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    Are they actually reading individual files off the file system (like grub), or are they reading a single archive (like lilo loading the initramfs)? Jan 17 at 7:09
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    @Luaan many Linux loaders like LILO also don't understand filesystems at all and just load sectors at a hardcoded offset. Even Grub supports that mode in case the embedded space for the second stage loader isn't available
    – phuclv
    Jan 18 at 13:00

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