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[ The PC Guide | Systems and Components Reference Guide | Hard Disk Drives | Hard Disk BIOS and Capacity Factors | Hard Disk Size Barriers ]

The FAT16 Partition Size (2.00 GiB / 2.15 GB) Barrier

The 2 GiB capacity barrier is, unlike most of the other barriers discussed here, a file system problem that has nothing to do with the BIOS. It is different than the 1.97 GiB barrier, which is BIOS-related, and is in many ways most similar to the older BIOS barriers that preceded the 504 MiB barrier.

The 2 GiB capacity barrier is a limitation on the size of disk volumes in the FAT16 file system. Due to the way that disks are set up using clusters, it is not possible to have more than 2 GiB in a single partition when using the DOS or Windows 3.x operating systems, or the first version of Windows 95 (sometimes called "Windows 95A"). Under Windows NT, the limit is 4 GiB instead of 2 GiB when using FAT partitions (NTFS partitions do not have this limitation). This is all discussed in great detail in the section on file system structures.

Note: Using 4 GiB FAT partitions under Windows NT requires the use of 64 kiB clusters. This is supported but non-standard, and will result in problems if you try to set up a system using other operating systems in addition to Windows NT.

If you put a hard disk over 2 GiB into a machine that is using regular FAT (16-bit FAT) under DOS, Windows 3.x or the first version of Windows 95, you can use all of it--assuming that you aren't limited by one of the other BIOS-related barriers mentioned in adjacent sections. However, to access the full contents of the disk, you must partition it into multiple pieces. Since this limitation is a function of the operating system, it affects IDE/ATA and SCSI hard disks equally.

This limitation does not apply to disks formatted using the newer FAT32 file system. FAT32 is an enhancement that was in fact created specifically to get around this problem, and was introduced in Windows 95 OEM SR2. It is also supported in Windows 98, Windows ME and Windows 2000. There is also the NTFS file system, supported by Windows NT and Windows 2000, which uses a completely different set of structures and can have truly enormous-sized partitions (tens of gigabytes).

Next: The 6,322 Cylinder (3.04 GiB / 3.26 GB) Barrier

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