Hardware Reference
In-Depth Information
Although ATA-1 had been in use since 1986, work on turning it into an official standard began in
1988 under the Common Access Method (CAM) committee. The ATA-1 standard was finished and
officially published in 1994 as “ANSI X3.221-1994, AT Attachment Interface for Disk Drives.”
ATA-1 was officially withdrawn as a standard on August 6, 1999.
Although ATA-1 supported theoretical drive capacities up to 136.9GB (2
28
-2
20
= 267,386,880
sectors), it did not address BIOS limitations that stopped at 528MB (1024 × 16 × 63 = 1,032,192
sectors). The BIOS limitations would be addressed in subsequent ATA versions because, at the time,
no drives larger than 528MB existed.
ATA-2 (ATA Interface with Extensions-2)
ATA-2 was a major upgrade to the original ATA standard. Perhaps the biggest change was almost a
philosophical one. ATA-2 was updated to define an interface between host systems and storage
devices in general and not only disk drives. The major features added to ATA-2 compared to the
original ATA standard include the following:
• Faster PIO and DMA transfer modes
• Support for power management
• Support for removable devices
• PCMCIA (PC Card) device support
•
Identify Drive
command that reports more information
• Defined standard CHS/LBA translation methods for drives up to 8.4GB in capacity
The most important additions in ATA-2 were the support for faster PIO and DMA modes, as well as
methods to enable BIOS support up to 8.4GB. The BIOS support was necessary because although
ATA-1 was designed to support drives of up to 136.9GB in capacity, the PC BIOS could originally
handle drives of up to 528MB. Adding parameter-translation capability now allowed the BIOS to
handle drives up to 8.4GB. This is discussed in more detail later in this chapter.
ATA-2 also featured improvements in the
Identify Drive
command that enabled a drive to tell
the software exactly what its characteristics are; this is essential for both Plug and Play (PnP) and
compatibility with future revisions of the standard.
ATA-2 was also known by unofficial marketing terms, such as Fast-ATA or Fast-ATA-2
(Seagate/Quantum) and EIDE (Enhanced IDE, Western Digital).
Although work on ATA-2 began in 1993, the standard was not officially published until 1996 as
“ANSI X3.279-1996 AT Attachment Interface with Extensions.” ATA-2 was officially withdrawn in
2001.
ATA-3 (ATA Interface-3)
ATA-3 was a comparatively minor revision to the ATA-2 standard that preceded it. It consisted of a
general cleanup of the specification and had mostly minor clarifications and revisions. The most
major changes included the following:
• Eliminated single-word (8-bit) DMA transfer protocols
• Added S.M.A.R.T. (Self-Monitoring, Analysis, and Reporting Technology) support for
prediction of device performance degradation
• Made LBA mode support mandatory (previously, it had been optional)
