IDE EIDE ATA Info

IDE
Integrated Drive Electronics (IDE) refers to any drive with the controller built-in. The interface most of us use, that we call IDE, is actually called ATA, or AT Attachment. Most drives today are IDE. Because the controller is on the drive itself less parts are needed and the signal pathways can be much shorter resulting in improved reliability of the drive. Integrating the controller is easier for the manufacturer because they do not have to worry about complying with another manufacturer's controller. Each drive is an independent entity.

ATA IDE

This is the most popular IDE form. CDC, Compaq, and Western Digital were the first to create the interface. They also decided to use the 40-pin connector. They were large drives of the 5.25" form, but were only 40MB. They were used in the early Compaq 386 systems, using WD controllers. Later, Compaq founded Conner. Conner produced drives for Compaq, but was later sold.

In the late 1980's, the ATA IDE was set as ANSI standard. This caused all manufacturer's to agree with a common design for the interface. Before this was done, many companies had produced their own variations. This sometimes makes it hard for us to make these older drives work with newer ones in the same system. Some areas of the ATA standard were left open to manufacturer's for their own commands so the standard is quite loosely set.


Dual Drives
 
One of the nice features introduced with ATA was the ability to operate two drives together in a chain. The primary drive is the master, and the second drive is the slave. On most drives, you tell it to be a master or a slave with a jumper on the drive. When two drives are on the same ribbon cable, all commands are received by both controllers. Each drive must respond only to commands meant for it. Setting the drive as either master or slave tells it to ignore the commands for the other drive.

If a CD-ROM drive is present it should be on a separate IDE channel from the hard drives. It can be placed on the same channel but it will slow down both devices. The standard configuration is to place the hard drive(s) on the primary channel and the CD-ROM on the secondary IDE channel.


ATA I/O
 
The ATA interface uses a 40-pin connector. In theory, plugging it in backwards can damage the drive and related circuitry, although I have done it (inadvertently) many times and the drive was never damaged . The ribbon cable carries signals to and from the controller, and should be no longer than 18 inches. The red stripe goes to the side closest to the power connector on most drives.


ATA Types
 

ATA-2 = EIDE (Enhanced IDE). This is an extension off the original ATA that includes features such as PIO and DMA modes. These are basically performance enhancing features and are discussed below. The main benefits of ATA-2 are increased capacity and faster data transfer.

Increased capacity is basically due to an advance in BIOS to work with drives larger than 504 MB. This limit was there basically because of the geometry in the drive. Newer enhanced BIOS are capable of using translation modes, thereby using different geometry when talking with the drive than when talking with the software. If your BIOS is dated around 1994 or later, it is probably enhanced. You can tell if it offers settings called LBA, ECHS, or Large, which are just three different methods of translation.

Faster data transfer is what everyone is after these days. ATA-2 offers several different modes for higher performance. Most drives today are capable of PIO Modes 3 and 4, which are very fast. PIO (Programmed I/O) modes determine the speed at which data is transferred to and from the drive.

 

 PIO Mode Transfer Rate ATA Ver.
0 3.3 MB/sec ATA-1
1 5.2 MB/sec ATA-1
2 8.3 MB/sec ATA-1
3 11.1 MB/sec ATA-2
4 16.6 MB/sec ATA-2

 

To run Mode 3 or 4, the IDE port must be on a VL-bus or PCI bus connection. Some newer boards with two IDE connectors only have the IDE 1 connected to the PCI bus, while the second IDE connector uses an ISA bus, only capable of Mode 2. One should look into this before buying a new motherboard.


Jumper Settings


 
Most IDE drives come in three configurations: Single drive, master, and slave. These are controlled by a small series of jumpers, usually on the rear of the drive. The single drive setting tells the drive it is alone in the system, and it responds to all commands. If it is configured as a master, this tells the drive there is a slave drive present, and the drive will respond to only master commands. If the drive is configured as a slave, it responds only to slave commands. Before the ATA IDE specification, there was no common method of master/slave relationships.


Install Serial ATA