Specific PC Drive Capacity Limits


A Track is a ring of data or Sectors that moves under a specific Head as the disk rotates. A Cylinder is made up of the vertically in-line or stacked rings of data that are moving under all the drive Heads. So while Cylinders and Tracks are not exactly the same thing, the size or value for Cylinders is the same as the size or value for Tracks.

[WWW Link]The PC Guide: Older Size Barriers
http://www.pcguide.com/ref/hdd/bios/sizeOlder-c.html    [New Window]
This page (at the pcguide.com site) provides information on legacy PC drive limitations, from before IDE or ATA drives existed.
[HTML format Notes]IDE Combined Addressing barrier
. . . 504MB (528 million Bytes) limit.
This limitation is caused by the BIOS Int 13 system call and the IDE (ATA) standard using different maximum values for Cylinder, Head and Sector (CHS).
[HTML format Notes]4096 Cylinder BIOS barrier
. . . 1.97GB (2.11 billion Bytes) limit.
Some BIOS-- developed before the second half of 1996-- limited the physical drive Cylinders to a 12 bit binary number, which supports a maximum of 4096 Cylinders or Tracks. (CMOS values 0 to 4095)
[HTML format Notes]FAT16 Logical Drive Size
. . . 2.00GB (2.15 billion Bytes) limit.
For Windows Me/98/95 and MS-DOS, the maximum size for a primary FAT16 partition or a logical FAT16 partition is 2GB. While the possible dramatic increase in "wasted" drive space, resulting from larger cluster sizes, also needs consideration.
[HTML format Notes]6322 Cylinders BIOS bug
. . . 3.04GB (3.26 billion Bytes) limit.
One of the most obscure size limitations, affecting only a small percentage of systems-- where attempting to set a cylinder value higher than 6322 may cause the PC to hang.
[Webpage Copy or 'Mirror']Phoenix BIOS 4.03/4.04 bug
. . . 3.05GB (3.28 billion Bytes) limit.
"Cylinder values from 6350 to 8322 (assuming 16 Heads, 63 Sectors) will cause lockup in CMOS (may unfreeze in a minute or so). Cylinder values from 8323 to 14671 will work, but the size displayed in CMOS setup will be wrong."
[HTML format Notes]8192 Cylinders DOS & BIOS limit
. . . 3.94GB (4.22 billion Bytes) limit.
DOS, and other older operating systems, cannot handle a Logical CHS (L-CHS, used by the BIOS Int 13 system call) with 256 Heads. Thus when the drive's Physical CHS (P-CHS, or the values marked on a drive) has 16 Heads, the maximum corresponding Cylinders or Tracks for that drive is 8192. (Maximum CMOS value 8191)
[HTML format Notes]Windows NT FAT16 Size limits
. . . 4.00GB (4.29 billion Bytes) limit.
For the Window NT family of operating systems, the FAT16 cluster size is limited to 64KB instead of 32KB. Thus Windows NT/2000/XP can use a maximum primary FAT16 partition, or logical FAT16 partition of 4GB. However, FAT16 volumes larger than 2GB are not reliably accessible from computers running Windows Me/98/95 or MS-DOS.
[HTML format Notes]240 Heads DOS & BIOS limit
. . . 7.38GB (7.93 billion Bytes) limit.
Using 15 physical drive Heads (P-CHS), to work-around the 8192 cylinder DOS & BIOS limitation, restricts the maximum number of Logical Heads (L-CHS) to 240. Thus for anything using CHS addressing instead of LBA, access could be limited to the first 7.38GB of each physical drive. And there are several circumstances or methods by which this 15 drive head work-around could be invoked, on a drive by drive basis.
[HTML format Notes]255 Heads DOS & BIOS limit
. . . 7.84GB (8.42 billion Bytes) limit.
If the hard drive is accessed using LBA, then the CHS addressing (L-CHS) provided to the operating system can simply use 255 heads to work-around the 8192 cylinder DOS & BIOS limitation.
[HTML format Notes]BIOS Int 13h CHS barrier
. . . 7.88GB (8.46 billion Bytes) limit.
The upper limit for how much drive space the BIOS Int 13h system call can access using a CHS address (L-CHS). This is a BIOS specification limitation, and not a hardware or ATA (P-CHS) limitation. While the BIOS CHS addressing can access up to the first 7.88GB on a larger capacity hard drive, all space beyond that should be accessed using LBA. This requires a BIOS supporting the Extended Int 13h functions, and an operating system that can use LBA addressing; or an operating system that can bypass the BIOS by directly accessing a drive.
[HTML format Notes]63 Sectors BIOS limit
. . . 31.5GB (33.8 billion Bytes) limit.
This capacity limitation occurs when the BIOS just uses 63 sectors for all CHS addressing situations.
[Webpage Copy or 'Mirror']Windows 95 Drive Size barrier
. . . 32.0GB (34.4 billion Bytes) limit.
"Hard disks and other media that are larger than 32 gigabytes (GB) in size are not supported in any version of Windows 95."
[HTML format Notes]XP/2000 FAT32 Formatting limit
. . . 32.0GB (34.4 billion Bytes) limit.
Windows XP and 2000 fully supports using a FAT32 partition over 32GB, but does not permit formatting a FAT drive over 32GB. If you attempt to format a FAT32 partition larger than 32 GB, the format fails near the end of the process with the following error message:  "Logical Disk Manager: Volume size too big."
[Webpage Copy or 'Mirror']Windows 98 FDISK bug
. . . 64.0GB (68.7 billion Bytes) limit.
When the original Windows 98 fdisk is used to partition a hard drive larger than 64GB, fdisk does not report the correct size of the hard drive. The updated Windows 98 fdisk is not designed for 48-bit logical block addressing (LBA), so it does not support ATA drives larger than 128GB (137 billion Bytes).
[HTML format Notes]Windows 98 SCANDISK & DEFRAG limit
. . . 127.53GB (136.9 billion Bytes) limit.
Windows 98SE has a default limitation of 128GB (137.4 billion Bytes) for ATA drives, because it only supports the ATA-5 28-bit LBA. Thus Windows 98 could theoretically use a 128GB partition, but a limitation of the Microsoft SCANDISK and DEFRAG programs reduces the practical size to 127.53GB (136.9 billion Bytes).
[HTML format Notes]ATA-5 Specification barrier
. . . 128GB (137.4 billion Bytes) limit.
The original LBA uses a 28-bit binary number to specify the sector number on a drive, resulting in a 128GB size limit. The current ATA-6 specification provides a new (separate) 48-bit binary field, to permit addressing sectors beyond the 128GB ATA-5 limit.

Windows XP / 2000 users: Chances are, you won't need to use Disk Manager. Since Windows 2000 and Windows XP scan the bus itself, ignoring the BIOS, your Operating System should see the full size of the drive. If you are installing a drive on a system using the Award 4.5x BIOS, then you should still follow the Ontrack Data International solution for [33.8 billion Bytes] BIOS lock-up advice to avoid having your hard drive hang during the drive detection stage of system startup (boot).

 IBM hard drive downloads: Disk Manager 2000  
[WWW Link]Windows 2000 48-bit LBA Support
http://support.microsoft.com/?kbid=305098    [New Window]
Note: The drive controller hardware must also support 48-bit LBA.
[WWW Link]Windows XP 48-bit LBA Support
http://support.microsoft.com/?kbid=303013    [New Window]
Windows XP SP1 and above fully supports 48-bit LBA, if the computer hardware also supports 48-bit LBA. The original Windows XP Home Edition or Windows XP Professional can enable Windows 48-bit LBA support by editing a registry setting.
[WWW Link]Fdisk.exe 512GB limit
http://support.microsoft.com/?kbid=280737    [New Window]


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Page Content Updated: 23 January 2006