Hardware Reference
In-Depth Information
in mind, manufacturers have traditionally released their largest capacity drives in SCSI
versions first. With the advent of SATA, however, the gap is quickly closing.
Because of the changes in 2001 to both ATA and SCSI, it will be many years before the
capacity limitations of either interface become a problem.
Operating System Limitations
MorerecentOSs,suchasWindowsVistaandWindows7,don'thaveproblemswithlarger
drives. However, older OSs might have limitations when it comes to using large drives.
Windows XP and earlier versions are limited in capacity to supporting drives less than
2.2TB per physical or logical (that is, RAID) drive, including all partitions. This is due to
reliance on the MBR partitioning scheme, which uses 32-bit sector numbering, limiting
a physical or logical drive to a maximum of 2
32
(4,294,967,296) total sectors. Windows
7 and Vista SP1+ support a newer partitioning scheme called GPT, which defines sectors
using64-bitnumbers,supporting2
64
(18,446,744,073,709,551,616)sectors,foramaxim-
um capacity of 9.44ZB (zettabytes or billion terabytes). In practical terms, this means that
if you are running XP, you can't normally utilize more than 2TB of a single drive or a
RAID array of multiple drives. However, Windows XP can use GPT formatted drives of
2.2TB or greater in capacity if a third-party GPT utility tool like the Paragon GPT Loader
(
www.paragon-software.com
)
is used.
Windows 98 supports large drives, but a bug in the FDISK program included with Win-
dows 98 reduces the reported drive capacity by 64GiB for drives over that capacity. The
solution is an updated version of FDISK that you can download from Microsoft. Another
bugappearsinthe
FORMAT
commandwithWindows98:Ifyourun
FORMAT
fromacommand
promptonapartitionover64GiB,thesizeisn'treportedcorrectly,althoughtheentirepar-
tition is formatted.
Windows 95 has a 32GiB hard disk capacity limit, and there is no way around it other
than upgrading to Windows 98 or newer. Additionally, the retail and upgrade versions of
Windows95(alsocalledWindows95OSR1orWindows95a)arefurtherlimitedtousing
only the FAT16 (16-bit file allocation table) file system, which carries a maximum parti-
tion size limitation of 2GiB. Therefore, if you had a 30GiB drive, you would be forced
to divide it into 15 2GiB partitions, with each appearing as a separate drive letter (drives
C:-Q: in this example). Windows 95B and 95C can use the FAT32 file system, which al-
lows partition sizes up to 2TiB. Note that because of internal limitations, no version of
FDISK can create partitions larger than 512GiB.
DOS generally does not recognize drives larger than 8.4GB because those drives are ac-
cessed using LBA, and DOS versions 6.x and lower use only CHS addressing.
