Re: Help installing Fedora
From: Richard Steven Hack (richardhack_at_prontomail.com)
Date: Tue, 20 Jan 2004 14:12:24 GMT
On Mon, 19 Jan 2004 12:30:21 GMT, email@example.com (P.T. Breuer)
>ATAPI and [E]IDE are distinct. [E]IDE = ATA.
Read this, Peter:
Enhanced IDE, also called EIDE, is a term that Western Digital coined
in 1994 to represent a particular set of extensions it devised to the
original AT Attachment standard. At that time, the official ATA
standard was rather limiting, and work was progressing towards the new
ATA-2 standard. Western Digital decided that it did not want to wait
for the new standard, and also that it could better position itself as
a market leader by creating a new feature set for (then) future
drives. The name "Enhanced IDE" was presumably selected to build upon
the common name for ATA then in popular use: IDE.
The original Enhanced IDE program included the following improvements
ATA-2 Enhancements: EIDE includes all (most?) of the improvements that
are defined as part of the ATA-2 standard, including the higher-speed
ATAPI: The EIDE definition includes support for non-hard-disk ATAPI
devices on the IDE/ATA channel. Note that at that time, ATAPI was not
part of the ATA standard at all.
Dual IDE/ATA Host Adapters: The EIDE standard specifically includes
support for dual IDE/ATA channels, allowing four IDE/ATA/ATAPI devices
to be used. (In fact, the ATA standard at the time never precluded the
use of two IDE/ATA channels; it just was not commonly done.)
EIDE has become a widely-accepted term in the industry, which would be
great if not for the fact that it is so incredibly confusing.
Objections to EIDE include the following issues:
Proprietary Standard: EIDE is not an official standard, and it
competed with other non-standard IDE/ATA terms like Fast ATA. Of
course, that criticism applies not just to EIDE.
Scope: Much of the criticism of the original EIDE program is that its
scope was too wide, and that it encompassed features that are really
the domain of the BIOS. For example, support for dual IDE/ATA host
adapters, meaning a secondary IDE/ATA channel, has nothing to do with
the interface or the hard disk itself. And ATAPI is a standard that is
defined for use with optical drives and other non-hard-disk devices,
which again requires BIOS and driver support and really has nothing to
do with the hard disk. At the time, other hard disk manufacturers not
only excluded these from their own standard proposals (such as Fast
ATA), they made a point of criticizing Western Digital for bringing
these issues into the interface discussion.
The Word "Enhanced": The choice of the word "enhanced" was
unfortunate, as it led to confusion in another area. At around the
same time that EIDE was introduced, the 504 MB hard disk size barrier
became a big issue. To work around this required an "enhanced BIOS".
Because of the fact that both of these phrases use the word
"enhanced", and because EIDE defines BIOS support standards, many
people have come to think of the terms as interchangeable when they
really are not. This has lead to claims that you need an enhanced IDE
interface to support disks over 504 MB, when you don't--you just need
an enhanced BIOS. As if this weren't bad enough, some companies
advertised add-in cards with enhanced BIOSes as "enhanced IDE cards"!
Redefinition: Since EIDE is Western Digital's term, they have the
right to change its meaning, and unfortunately, they do this on a
regular basis. At first, EIDE included only PIO modes up to mode 3;
then mode 4 was added. When the new Ultra DMA modes came out, WD of
course added support for them to their newest models, but they kept
calling the drives "EIDE"! Today other drive manufacturers also say
things like "EIDE compatible", leaving you wondering what exactly this
Some people in the hard disk industry apparently feel that the
creation of "Enhanced IDE" was one of the worst things to ever happen
to the IDE/ATA interface! I think that is probably a bit over-stated,
though I do agree that it is probably one of the most confusing things
to ever happen to the IDE/ATA interface. :^) Much of the criticism is
valid, but some of it is just the usual conflicts between rivals in a
very competitive industry. And I do think Western Digital's goal of
expanding IDE/ATA capabilities was a laudable one, even if the
implementation of the program left a bit to be desired.
Of all the criticisms leveled at Western Digital, there's one that I
personally agree with strongly, and that's the issue of redefining the
term. Every time the IDE/ATA interface standards change, Western
Digital changes the actual interface specifics of its drives, but
continues to list the interface of the drive as just "EIDE". A term
that is constantly redefined is a term that is utterly meaningless. As
a result, I can only tell people at this point that if they see a
drive labeled as being "EIDE", to keep digging to find out the
specifics of the modes and official standards it supports, because
"EIDE" by itself doesn't tell you anything (other than the generic
interface of the drive, as the terms "IDE" or "ATA" do.) It would be
nice if Western Digital would just drop the term entirely, but I doubt
this will happen since they have spent so many years promoting it
Read this, Peter:
Unfortunately, because of how the ATA command structure works, it
wasn't possible to simply put non-hard-disk devices on the IDE channel
and expect them to work. Therefore, a special protocol was developed
called the AT Attachment Packet Interface or ATAPI. The ATAPI standard
is used for devices like optical, tape and removable storage drives.
It enables them to plug into the standard IDE cable used by IDE/ATA
hard disks, and be configured as master or slave, etc. just like a
hard disk would be. <==== See this, Peter? When you see a CD-ROM or
other non-hard-disk peripheral advertised as being an "IDE device" or
working with IDE, it is really using the ATAPI protocol.
Internally, however, the ATAPI protocol is not identical to the
standard ATA (ATA-2, etc.) command set used by hard disks at all. The
name "packet interface" comes from the fact that commands to ATAPI
devices are sent in groups called packets. ATAPI in general is a much
more complex interface than regular ATA, and in some ways resembles
SCSI more than IDE in terms of its command set and operation. (At the
time it was created, SCSI was the interface of choice for many CD-ROM
and higher-end tape drives.)
A special ATAPI driver is used to communicate with ATAPI devices. This
driver must be loaded into memory before the device can be accessed
(most newer operating systems support ATAPI internally and in essence,
load their own drivers for the interface). The actual transfers over
the channel use regular PIO or DMA modes, just like hard disks,
although support for the various modes differs much more widely by
device than it does for hard disks. For the most part, ATAPI devices
will coexist with IDE/ATA devices and from the user's perspective,
they behave as if they are regular IDE/ATA hard disks on the channel.
<===== See this, Peter? Newer BIOSes will even allow booting from
ATAPI CD-ROM drives.
The first ATAPI standard document produced by this group was called
SFF-8020 (later renamed INF-8020), which is now quite old and
obsolete. In the late 1990s, the T13 Technical Committee took over
control of the ATAPI command set and protocol, combining it with ATA
into the ATA/ATAPI-4 standard.
Now cite me something different, Peter, if you can.
The above is from http://www.pcguide.com/ref/hdd/if/ide/index.htm
which by the way is the source for the storagereview.com article.
-- Richard Steven Hack "Whatever does not kill me makes me stronger" - and YOU have not killed me!