Frequently Asked Questions about the IDE/EIDE Drive Interface

Frequently Asked Questions

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This is a general description of the most frequently asked questions about the IDE/EIDE Interface. This information is meant only to address basic troubleshooting of IDE/EIDE compatibility issues, and is not meant to be an in-depth discussion of all possible error issues. Our purpose is to aid you in solving basic IDE/EIDE difficulties that may arise.

Notice: The information provided herein is presented as is and without any warranty of any kind, either expressed or implied. In no event will DEW Associates Corporation be liable to you for any damages, including any loss of profit or other money damages, arising out of the use or inability to use the information contained herein. We make no representations or warranties with respect to the contents hereof and specifically disclaims any implied warranties of merchantability or fitness for any particular purpose. Any parameters and specifications provided are subject to change without notice.

Issues Covered:

  • IDE/EIDE Definitions
  • Compatibility Issues
Q01: What is IDE/ATA?
A01: Integrated Drive Electronics (IDE) is a generic term applied to any drive with an integrated (built-in) disk controller. The first drives with integrated controller were Hardcards. In the IDE architecture, the disk controller is integrated into the drive. This combination drive/controller assembly usually plugs into an interface on the motherboard or an interface card plugged into an empty bus slot. The ATA Specification is simply a set of rules or guidelines that an IDE drive should conform to.
NOTE:  The current revision of the ATA specification is ATA-7.
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Q02: What does the IDE interface actually do?
A02: The primary job of the IDE interface is to transmit/receive data to and from the drive.
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Q03: Why place the Controller on the drive itself?
A03: Placing the controller on the drive gives IDE drives built-in reliability because data encoding, from digital to analog is performed directly on the drive in a tight, noise-free environment. The timing-sensitive analog information does not have to travel along ribbon cables that may pick up noise and insert propagation delays into the signals. The integrated configuration allows for increases in the clock rate of the encoder, as well as the storage density of drive.
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Q04: What is Enhanced-IDE (EIDE) and Fast-ATA?
A04: Enhanced IDE (EIDE) was a marketing program first initiated by Western Digital. EIDE has two sides:

  • Software – the Enhanced BIOS Specification that surpasses the 504 MB hard drive capacity limitation
  • Hardware – hard drives that conform to the ATA-2 and ATA-PI Standards

Fast-ATA, EIDE’s counterpart, was a separate marketing program that was introduced by Seagate and Quantum. This program leaned conservatively toward the ATA-2 specification.

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Q05: What are the main features of EIDE
A05: These are the main features:

  • Faster transfer modes- PIO modes 3-4, DMA mode 2 and UDMA.
  • Multiple Read/Write commands
  • LBA mode, translation for drives larger than 504 MB
  • Four devices on the ATA controller (secondary port)
  • CD ROM and Tape Drive support
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Q06: Is ATA-5, 6 or 7 compatible with older IDE drives?
A06: Older IDE peripherals will work with newer enhanced drives. However you will not be able to fully utilize the enhanced features of your ATA-5, 6 or 7 peripherals.
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Q07: Is ATA-5, 6 or 7 compatible with older IDE controller cards?
A07: EIDE drives are backward compatible with non-EIDE (standard) controller cards. However, an EIDE card will only perform at the capabilities of the controller; hence the EIDE drive will perform like a standard IDE drive.
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Q08: What is ATA-PI
A08: AT Attachment Packet Interface (ATA-PI) is a standard that implements SCSI like devices on the ATA bus. Devices like CD-ROM’s, tape drives and other removable media. The advantages of ATAPI are:

  • It is inexpensive
  • It is easy to implement in current systems.

ATAPI’s disadvantage is that it requires the use of software drivers for operability.

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Q09: What is Cable Select (CSEL)?
A09: Cable Select (CSEL) is an optional feature per the ANSI ATA specification. It is an alternative method of identifying the difference between device 0 and device 1 on an IDE interface cable. Hard drives configured in a multiple drive system are identified by CSEL’s value:

  • If CSEL is grounded, then the drive address is 0.
  • If CSEL is open, then the drive address is 1.

Additionally, CSEL requires a specialized (and more expensive) 40-pin 80-wire IDE interface cable, unlike the standard EIDE interface cable that is far more commonly used. We do not recommend using the CABLE SELECT feature unless your specific computer system documentation requires its use.

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Q10: How does my computer know which drive is the Master and which is the Slave?
A10: When only one drive is installed, the single drives controller responds to all commands from the system. When two drives (which means two drive controllers) are installed, both controllers receive all commands from the system. Each drives controller must then be configured to respond only to commands issued to it. In this situation, one controller must be designated as master and the other as slave. When the system sends a command to a specific drive, the other drive’s controller must remain silent. A special bit (the DRV bit) is used in the Drive/Head Register to distinguish between the controllers.
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Q11: Why is the 20th hole plugged on the Ribbon Connector?
A11: It is a means of preventing the cable from being installed (plugged in) upside down. Users that inadvertently plug a cable in backwards can cause damage to both the hard drive and the motherboards interface. If your system does not have the corresponding missing pin, you may remove this plug by “teasing it out” with a straight pin.
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Q12: Does the IDE interface cable influence data integrity, signal noise issues and drive recognition?
A12: The answer is Yes! The ATA standard specifies that an IDE Interface cable should be no longer than 18 inches. The standard cable used today conforms to the ATA specifications. However, 40 pin interface cables do not always filter out noise when used with the Ultra DMA 33, 66, 100 and even 133 hard drives of today. Another option for reduction of cable noise would be to use an 40-pin 80-wire interface cable. These cables provide better grounding to maximize signal integrity.
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Q13: Will adding an EIDE Interface increase disk performance?
A13: Although most, if not all computers manufactured today have the fastest interface available, the answer really depends on the hard disk drive. Unless you’re working with legacy equipment, a new interface may not give you a performance increase. As an example, upgrading an ISA controller to a PCI controller would be the biggest improvement a user could make.
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Q14: Why is the hard disk drive NOT as fast as advertised?
A14: Advertised transfer rates are based on the fastest speed at which the drive can send data across the ribbon cable from the drive buffer, with the transfer stopping temporarily every time the buffer re-fills. This process continues until a command is complete. Data transfer rates will differ between system configurations, as a drive is not the single component that decides transfer rates. The one thing that designers have control of is the speed at which data transmits across the data ribbon cable from the drive’s buffer, but not how your other components interact with the drive.
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Q15: Why is it that an old IDE drive may not work with a New IDE drive?
A15: The reason is the fact that many hard drive manufacturers were already making and selling drives before the IDE standard was clearly defined. While this is now, for the most part, relegated to very old IDE drives that have problems functioning in dual-drive configurations. This scenario was more prevalent when the hard disk drives are from different manufacturers, however, in some cases, two drives may not function together at all. Even today though, in rare circumstances even new drives will not work together.
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Q16: Why is my new IDE drive not recognized as a slave or a master?
A16: Configuring IDE drives can be simple, as is the case with most single-drive installations, or troublesome, especially when mixing drives from different manufacturers on a single cable. Most IDE drives must be configured in one of the following ways:

  1. Single-drive (master)
  2. Master in a dual-drive system
  3. Slave in a dual-drive system

Because each IDE drive has its own controller, one drive must be jumped as a master and the other as the slave. There are no functional differences between the two, except that the drive that’s specified as the slave will assert the DASP (Drive Active/Slave Present) signal after a system reset to inform the master that a slave drive is present in the system. Daisy-chained hard disk drives that do not have their jumpers set correctly will not function. You should contact the disk drive manufacturer if you are unsure of proper jumper settings.

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Q17: Two hard disk drives will not function even after verifying jumper settings. What could be wrong?
A17: There may be a compatibility problem between the two drives. Use the following steps to verify the function of each drive:

  1. Test each drive by itself, making sure that each drive has been jumpered correctly. If both drives work by themselves, you may conclude that there is a compatibility problem.
  2. Try “swapping” (switching) the drive’s position, what was the master will be changed to a slave and the slave will become the master.
  3. Most motherboards have two IDE bus connectors. Place one drive on each IDE bus and test the system.
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Q18: Why does an IDE CD-ROM and Tape Backup not work when attached to the Interface?
A18: On  occasion, attaching an IDE CD-ROM or tape backup drive to a bus that supports an IDE drive, can slow down and even compromise the drive’s data integrity. Although this is extremely rare today, make sure that your systems motherboard has an Enhanced IDE interface that is ATAPI compliant. If it is not, you can purchase and add-in card that has this interface, and they usually come with a secondary IDE interface built on the same card.
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Q19: Even after switching roles, my hard drives still will not work. What else can I do?
A19: First, see questions 16 and 17 above. We recommend that you separate the hard drives and connect them to the different interface ports (IDE buses) of the system. If the system does NOT have a Secondary IDE interface, we recommend that you install an EIDE interface card. By doing so, each of your drives would be able to communicate individually with the system. Enhanced EIDE cards also can add BIOS LBA support and enhanced performance for the drives.
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Q20: Why are 80-wire, 40-pin ribbon cables required for certain hard drive configurations?
A19: 40-conductor cables support only up to 33MB/sec transfers (and should only be used for up to 16MB/sec or less in our opinion), while 80-conductor cables support up to 100MB/sec. Thus you can always replace a 40-conductor cable with an 80-conductor cable, but not the other way around without seriously hurting transfer speeds, and quite possibly damaging one or more of your systems components.
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