Windows NT Partitioning Rules During Setup

This article was previously published under Q138364
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During the installation of Windows NT, Setup determines the best partitioning scheme to use based on the existing partition table entries and where you choose to install Windows NT. Windows NT Setup restraints restrict the boot partition of up to 4 GB. The limit may be smaller depending on disk geometry. The actual value that is used as the limit is whatever Setup believes to be 1024 cylinders worth of disk space. Sometimes this is 1 GB, 2 GB, or 4 GB, but can be some other value depending on the make, model, and configuration of the hard disk adapter in use. This is the amount of space with which the text-mode portion of the installation can work. From this amount, you can create partitions that do not exceed 4 GB because the partition must first be formatted FAT and this file system has a limit to 4 GB.

Note: Windows 2000 and later operating systems no longer have a 4GB system / boot partition limit, however the partition types that Setup creates still follow the rules described in this article.

For additional information, click the following article numbers to view the articles in the Microsoft Knowledge Base:
119497 Boot Partition Created During Setup Limited to 4 Gigabytes
224526 Windows NT 4.0 Supports Maximum of 7.8-GB System Partition
These articles explain rules to consider before you install Windows NT 4.0 on computers that contain large hardware RAID-5 drive arrays if you want to use the full contiguous capacity of these large arrays after Windows NT4.0 is installed.
When you use a Hardware RAID-5 configuration, it is very important to understand how Windows NT partitions your drive during Setup in order to maintain maximum contiguous capacity of the large Array for user data after Windows NT is installed. Setup follows these rules:

Rule 1

If no partitions pre-exist on the drive, Setup makes the primary partition the size you specify for Windows NT (up to 4GB).

Rule 2

If a primary partition already exists, and you choose to install Windows NT in an unformatted free space, you are prompted for the size of the partition to create (up to 4 GB). After you choose the partition size, Setup creates the largest extended partition possible (up to 7.8 GB if using a 63 sectors/track, 255 tracks/cylinder translation scheme) and creates a logical drive within the extended partition of the size you choose. After Windows NT is installed, the unused extended partition space can be used for additional logical drives.

Rule 3

If a primary and extended partition already exist and free space in the extended partition is selected, Windows NT creates a new logical drive of the size specified by you.

Rule 4

If a primary and extended partition already exist and free space is available and selected outside of the extended partition, Windows NT creates another primary partition of the size the you choose (up to 4GB) for Windows NT to be installed in.

There are two possible workarounds:
  • Prior to installing Windows NT, use MS-DOS FDISK to create an extended partition of 250 MB, then create a logical drive of 250 MB within the extended partition. When you install Windows NT, select this partition as the target to install Windows NT in.

  • Install Windows NT into the first primary MS-DOS FAT partition. After Windows NT is installed, run Disk Administrator and create a second primary partition of 250 MB. Re-install Windows NT into this second primary partition and then delete the first Windows NT installation from the first primary MS-DOS partition.


You have four 2-GB drives configured in a hardware RAID-5 configuration for a total capacity of 6 GB and want a 5.5-GB NTFS partition for user data after Windows NT is installed. You have MS-DOS pre-installed on a 250-MB primary partition prior to installing Windows NT and want to keep this intact. You decide to install Windows NT into a separate NTFS partition and create a 250-MB partition from free space during Windows NT Setup.

Using rule 3 above, Windows NT creates an extended partition of 4 GB, then creates a 250-MB logical drive within to install Windows NT on. After Windows NT is installed, Disk Administrator shows the following:
   C:   250   MB FAT   D:   250   MB NTFS (logical drive)      3.750   GB extended partition space (free)      1.750   GB Free space      -----      6.0     GB total usable space in hardware raid-5 configuration.				
The problem is that the 2 free spaces cannot be combined to equal the 5.5-GB partition space wanted for user data.


Article ID: 138364 - Last Review: 12/04/2015 12:11:56 - Revision: 3.2

Microsoft Windows 2000 Server, Microsoft Windows 2000 Advanced Server, Microsoft Windows 2000 Professional Edition, Microsoft Windows NT Advanced Server 3.1, Microsoft Windows NT Server 3.5, Microsoft Windows NT Server 3.51, Microsoft Windows NT Server 4.0 Standard Edition, 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 Advanced Server 3.1, Microsoft BackOffice Small Business Server 2000 Service Pack 1

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