Hardware Reference
In-Depth Information
into the ATA-4 specification that was finally published in 1998. A separate BIOS firmware interface
specification called Protected Area Run Time Interface Extension Services (PARTIES) was initiated
in 1999 that defined services an operating system could use to access the HPA. The PARTIES
standard was completed and published in 2001 as “NCITS 346-2001, Protected Area Run Time
Interface Extension Services.”
The HPA works by using the optional
ATA SET MAX ADDRESS
command to make the drive
appear to the system as slightly smaller. Anything from the new max address (the newly reported end
of the drive) to the true end of the drive is considered the HPA and is accessible only using PARTIES
commands. This is more secure than a hidden partition because any data past the end of the drive
simply cannot be seen by a normal application or even a partitioning utility. Still, if you want to
remove the HPA, you can use some options in the BIOS Setup or separate commands to reset the max
address, thus exposing the HPA. At that point, you can run something such as Parted Magic or
Partition Commander to resize the adjacent partition to include the extra space that was formerly
hidden and unavailable.
Starting in 2003, some systems using Phoenix BIOS have included recovery software and diagnostics
in the HPA. Most if not all current drives support the HPA command set; however, because of the
complexity in dealing with the hidden area, I have seen most manufacturers back away from using the
HPA and revert to a more standard (and easier to deal with) hidden partition instead.
For more information on the HPA and what might be stored there, see the
Chapter 5
section,
“
Preboot Environment
,
”
p.
287
.
ATAPI
ATAPI is a standard designed to provide the commands necessary for devices such as optical drives,
removable media drives such as SuperDisk and Zip, and tape drives that plug into an ordinary SATA
or PATA (IDE) connector. Although ATAPI optical drives use the hard disk interface, they don't
necessarily look like ordinary hard disks. To the contrary, from a software point of view, they are a
completely different kind of animal. They most closely resemble a SCSI device. All modern ATA
optical drives support the ATAPI protocols, and generally the terms are synonymous. In other words,
an ATAPI optical drive is an ATA optical drive, and vice versa.
Caution
Most systems starting in 1998 began supporting the Phoenix El Torito specification, which
enables booting from ATAPI CD or DVD drives. Systems without El Torito support in the
BIOS can't boot from an ATAPI CD or DVD drive. Even with ATAPI support in the BIOS,
you still must load a driver to use ATAPI under DOS or Windows. Windows 95 and later
(including 98 and Me) and Windows NT (including Windows 2000 forward) have native
ATAPI support. Some versions of the Windows 98 and Me CD-ROMs are bootable, whereas
all Windows NT, 2000, and newer discs are directly bootable on those systems, thus greatly
easing installation.
ATA Drive Capacity Limitations
ATA interface versions up through ATA-5 suffered from a drive capacity limitation of about 137GB
(billion bytes). Depending on the BIOS used, you can further reduce this limitation to 8.4GB, or even
