There's an old joke that says the great thing about standards is that there are so many
to choose from. Anyone who has tried to understand hard disk interface standards knows
exactly what this means. 
To help you comprehend what can be a very confusing subject,
I have spent considerable time researching all of the issues related to IDE/ATA standards,
and have presented them here in what I hope is fairly plain English.
Standards probably get just a bit too much flak. Despite the confusion that standards
can cause, that's nothing compared to the confusion caused by a lack of
standards. So it was in the early days of the IDE/ATA interface. During the late 1980s,
IDE/ATA grew in popularity, but there were no standards in place to ensure that the
interface decisions made by different hardware companies were compatible with each other.
Several manufacturers succumbed to the temptation to make slight "improvements"
to the interface. As a result, many early IDE/ATA drives exhibited compatibility problems,
especially when one attempted to hook up a master and slave device on the same cable.
Recognizing the potential for utter chaos here, a number of designers and manufacturers
of hard disks and related technology got together to form the Common Access Method
(CAM) committee on the AT Attachment interface. The first document describing the
proposed IDE/ATA standard was introduced in early 1989. It was submitted in 1990 to the
American National Standards Institute (ANSI), and eventually became the first formal ATA
standard. The CAM committee was eventually replaced with other similar groups charged with
the various tasks associated with managing the IDE/ATA interface.
Today, ATA standards are developed, maintained and approved by a number of related
organizations, each playing a particular role. Here's how they all fit together:
- American National Standards Institute: ANSI
is commonly thought of as an organization that develops and maintains standards, but in
fact they do neither. They are an oversight and accrediting organization that facilitates
and manages the standards development process. As such, they are the "high level
management" of the standards world. They qualify other organizations as Standards
Developing Organizations or SDOs. ANSI also publishes standards once they
have been developed and approved.
- Information Technology Industry Council: ITIC
is a group of several dozen companies in the information technology (computer) industry.
ITIC is the SDO approved by ANSI to develop and process standards related to many
computer-related topics.
- National Committee for Information Technology: NCITS is a committee established by ITIC to
develop and maintain standards related to the information technology world. NCITS was
formerly known under the name "Accredited Standards Committee X3, Information
Technology", or more commonly, just "X3". It maintains several
sub-committees that develop and maintain standards for various technical subjects.
- T13 Technical Committee: T13
is the actual technical standards committee responsible for the IDE/ATA interface
specifically.
So basically, T13 is the group that actually does the work of developing new IDE/ATA
standards. ;^) The T13 group is comprised primarily of technical people from various hard
disk and other technology companies, but the group (and the development process itself) is
open to all interested parties. Comments and opinions on standards under development are
welcomed from anyone, not just T13 members. The standards development process is intended
to create consensus, to ensure that everyone who will be developing hardware and software
agrees on how to implement new technology.
Once the T13 group is done with a particular version of the standard, they submit it to
NCITS and ANSI for approval. This approval process can take some time; which is why the
official standards are usually published several months, or even years, after the
technology they describe is actually implemented. While approval of the standard is
underway, companies develop products using technology described in the standard, confident
that agreement has already been reached. Meanwhile, the T13 group starts work on the next
version of the standard.
Now that you understand how the standards process works, you are in much better shape
to read the rest of this section, which describes all of the different standards that
describe the IDE/ATA interface. They are listed in approximately chronological order.
Remember when reading that subsequent standards build upon earlier ones, and that in
general, hardware implementing newer standards is backward-compatible with older hardware.
Note: Standards that have
been approved and published by ANSI are available for purchase in either print form or
electronic format from ANSI's web site. Draft
standards that are under development (as well as older drafts of approved standards) can
be found at the T13 Technical Committee web site.
Tip: If there's an IDE/ATA
standard you are looking for information on but can't find in this section, it might in
fact be an "unofficial" standard or marketing term.
Next: ATA (ATA-1)
