What is the biggest disk NT can use?

A. The simple answer to this question is that NT can view a maximum partition size of 2 terabytes (or 2,199,023,255,552 bytes), however there are limitations that restrict you well below this number.

FAT has internal limits of 4 GB due to thefact it uses 16-bit fields to store file sizes, 2^16 is 65,536 with a cluster size of 64 KB gives us the 4 GB.

HPFS uses 32bit fields and can therefore handle greater size disks, but the largest single file size is 4GB. HPFS allocates disk space in 512 byte sectors which can cause problems in Asian markets where sector sizes are typically 1024 bytes which means HPFS cannot be used.

NTFS uses 64-bits for all sizes, leading to a max size of..... 16 exabytes!!! (18,446,744,073,709,551,616 bytes), however NT could not handle a volume this big.

For IDE drives, the maximum is 136.9 GB, however for a standard IDE drive this is constrained to 528MB. The new EIDE drives can access much larger sizes.

It is important to note that the System partition (holding ntldr, boot.ini, etc.) MUST be entirely within the first 7.8Gb  of any disk (if this is the same as the boot partition this limit applies) This is due to the BIOS int 13H interface used by ntldr to bootstrap up to the point where it can drive the native HDD IDE or SCSI. int 13H presents a 24 bit parameter for cylinder/head/sector for a drive. If say by defragmentation the system are moved beyond this point you will not be able to boot the system.

The 7.8GB limit is only true on an IDE-type drive if the heads=255 and sectors=63. The real limit is the 1024 cylinder limit. If, for example, the heads=16 (as some IDE drives insist on) then the files mentioned must live within the first 504MB. This whole BIOS/big disk situation is getting worse and worse recently as manufacturers GHOST images onto 20GB and 30GB single-partition volumes, and do it on machines without the BIOS INT13support for a volume that size.

The boot process starts with your BIOS (Basic Input/Output System), notWindows NT.

The BIOS locates the beginning of a partition by using three numbers, theStarting Side (or Head), the Starting Cylinder, and the Starting Sector.

The end of a partition is identified by three similar numbers. The Side valueis 8 bits with a range from 0 to 255 (256 numbers); the Cylinder is 10 bits, andcan range from 0 to 1023 (1024 numbers); the Sector is 6 bits, and can rangefrom 1 to 63 (63 numbers). (Note that zero is not a valid sector number.) Thismeans the maximum address on the disk is Side 255, Cylinder 1023, Sector 63. Thenumber of sectors is 256 X 1023 X 63, or almost 16.5 million sectors. Standardsectors are 512 bytes, so hence the size of 7.87GB in which the system filesmust reside in.

Windows 2000 has no such limitation.  These are limits imposed by the specific machine BIOS.  Newer machines/BIOSes typically don't have this limitation.