Ntfs Partition Limit Code To Read

Over 1,000,000 fellow IT Pros are already on-board, dont be left out.

If you preformat the NTFS partition in another NT box or use a 3rd party utility that can create and format NTFS partitions such as PartitionMagic or ServerMagic, then the boot partition can be up to 7.8GB in size.

This is the summary you will often see in newsgroups.

When the computer boots, the only way for Windows NT to access the hard drive is to use a set of BIOS functions known as Interrupt (INT 13).

When INT 13 was developed, multigigabyte hard drives werent available and INT 13s limitation of 7.8 GB wasnt seen as critical.

As a consequence, Windows NT 4.0 cant access more than 7.8 GB during the first stages of the boot process; thus, the system partition is limited to 7.8 GB.

Newer operating systems such as Windows 98 and Windows 2000 dont suffer from this limitation because they use a newer extended INT 13 that can address more than 7.8 GB.

During Windows NTs boot process, ntdetect.com, uses int13 BIOS function for drive layout information.

Because of int13 limitations, ntldr, boot.ini, ntdetect.com and Windows NTs system files must be located within the first 1024 cylinders of drive 0.

Ntfs Partition Limit Code To Read

The int13 functions allow low-level code to read from and write to the drive.

These functions use 24 bits to address sectors on the hard disk.

The maximum amount of sectors accessible to the INT 13 interface is therefore: Cylinders heads sectors 1024 256 63 16,515,072 When the sectors size is 512 bytes, this calculated to 16,515,072 512 8,455,716,864 bytes 7.875 GB.

The above assumes a disk standard geometry with 63 sectorstrack, 256 heads with 1024 cylinders.

Some drives are configured with 63 sectorestrack, 128 heads with 2048 cylinders.

This is an access limitation during boot to the first 1024 cylinders.

For the drives configured with 2048 cylinders, fully half its space is unavailable during boot, resulting in a maximum usable NT system partition of 4GB.

This leads to significant confusion about the maximum size for NT system partition.

As you can see, its either 4GB or 7.875GB depending on whether the drive is configured with 2048 cylinders or 1024 cylinders under NTFS.

If you dont know which applies to your drive, use 4GB as your C partition.

A related issue involves dual-boot for Windows NT and Win95Win98.

Win9x must be installed on a FAT16 partition (since NT will not boot to fat32) which constraints the boot partition down to 2GB.

The size of a cluster must be a power of 2 and less than 65,536 bytes--this results in a maximum cluster size of 32,768 bytes (32K).

The problem is that NT will install properly and run fine even in the drive with 2048 cylinders if you create a large partiton, even a 18GB or 21GB.

During the install, Windows files used during the boot process are compacted in the early sectors.

Lets say you have mostly filled your HD and the that next niffty service pack comes along and up apply it.

Unfortunately at this point, the updated dlls and other system files are spread across the entire partition.

If any of the critical files are stored above the 1024 cylinder limit, on your next boot, you will get the thrilling message, INACCESSIBLEBOOTDEVICE.