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Article ID: 119497 - Last Review: February 28, 2014 - Revision: 2.1

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The size of the boot partition generated by Windows NT setup is limited to 4 gigabytes (GB) because Windows NT Setup must first format the partition to the FAT file system. Although it is possible to select NTFS for the boot partition during Setup, this partition is first formatted to FAT, Setup completes, then the partition is converted to NTFS. Because the FAT file system is limited to a 4-GB partition size, the boot partition for Windows NT is also effectively limited to 4 GB.


Windows NT versions 3.1 and 3.5 Setup does not load the full Windows NT Kernel and related drivers, so it is not possible for Setup to read an NTFS partition. During setup, even if you choose NTFS for the boot partition, it must be formatted to FAT (limited to 4 GB) so that Setup can write to it. Thus, the Windows NT boot partition is limited to 4 GB.


Move the hard drive to another system running Windows NT and attach it to the same make, model controller as on the original system. Run disk administrator and make a larger NTFS partition of up to 7.8gb formatted. As long as the drive is being translated, the partition table entry should contain valid starting Cylinder, Side, and sector values used for booting. The drive can then be moved back to the original system and ready for Windows NT installation.

Starting and Ending Cylinder, Side, and Sector

The Starting and Ending Side, Cylinder and Sector fields are very important with respect to how Windows NT interacts with the disk.

The maximum number of Sides (read/write heads) that can be represented with 1 byte is 256. The maximum number of Cylinders that can be represented with 10 bits is 1024. The maximum number of Sectors that can be represented with 6 bits is 63 because Sectors start counting with 1 (versus Cylinders and Sides which start counting with 0).

With a standard sector size of 512 bytes, the 24 bits used to record the starting and ending sector addresses translates into a maximum possible partition size of 7.8GB (8,455,716,864 bytes) which can be described with these fields. This is particularly important because the same field sizes are employed by the INT 13 BIOS interface which defines how the system BIOS interacts with the hard disk and is used while booting.

For additional information on file system limits in Windows NT, please see the following article in the Microsoft Knowledge Base:
ARTICLE -ID: 114841  ( )
TITLE : Windows NT Boot Process and Hard Disk Constraints

  • Microsoft Windows NT Advanced Server 3.1
  • Microsoft Windows NT Workstation 3.1
  • Microsoft Windows NT Workstation 3.5
  • Microsoft Windows NT Workstation 3.51
  • Microsoft Windows NT Workstation 4.0 Developer Edition
  • Microsoft Windows NT Server 3.5
  • Microsoft Windows NT Server 3.51
  • Microsoft Windows NT Server 4.0 Standard Edition
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