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Connecting IDE Hard Drives

You Would Think It Was Simple, But...

When connecting IDE devices in your computer, there are a few rules you need to know about.

First, Master and Slave devices are different for the 80-wire cables and the 40-wire cables.

Second, if you don't know for sure, RTDM... (read the damn manual).

Inside your computer, you generally have two (2) IDE hard drive controller connections. They look this this 99% of the time:

Yup, this is a picture...

[ The smaller one on the very top is a floppy drive controller connection ]

There is a Primary & Secondary connection located here. The Primary connection ALWAYS gets the 80-wire cable. Most of the time, but not always, you connect the 40-wire cable on the other Secondary connection. This is normally where you connect your lesser used devices like CDROMs, CDROM Burners and Tape Drives. You can connect other hard drives here with your CDROM or slower device, but there are issues that I'll go into later.

Pictured here are the two cables, the 80-wire and the older 40-wire ATA IDE cables. As you can see, the one on the left, the newer 80-wire cable has very small wires running from connector to connector, conversely, the 40-wire cable has larger wires. There is a reason for this. The newer standard requires the addition and separation of the wires for better signals to achieve the faster speeds.

The older Master & Slave relationship

For the longest time, hard drives have always had a setting for a Master or Primary setting and Slave. The Master was always the boot drive, the drive that contained the operating system. The other drive or Slave drive was for data storage. In rare cases, using this configuration you could boot from a Slave device but I'm not gonna get into that here and now. The way technicians have always done it in the past with the 40-wire cable was Master in the Middle connection and Slave on the end. It really didn't matter much until the hard drive makers started making drives with the Cable Select option.

Okay, lets set the record straight. The 80-wire cables are not called 80-pins! Burn this in to your brain kids. The older 40-wire and the newer 80 wire are both 40-pins! Well, actually, their 39 pins. One pin was removed that was never used so people installing hard drives wouldn't connect them backwards. If you scroll up and look at the motherboard connector at the beginning of this article, you'll see the 19th pin removed so that these cables can't be connected the wrong way. See the picture below...


Connecting Your Hard Drives

40 Wire Cables
On the slower older 40-wire ATA cables, the Master device, usually a CD-ROM or CD-ROM recorder/burner still goes on the END, but you need to set the jumpers as Slave. Did you ever buy a new CDROM or CDROM burner, open up the package and see that the jumper was already on the Slave position? It's that way for a reason. This is true even if you don't have a hard drive in the Master position. The Master for 40-wire cables goes on the the Middle connector. Only older computers (the AT type) have a problem here, and again, you should read the manual that came with the motherboard or contact the maker of the system. You could try it as a Master and it may work but that's not the way it should be. If you want to use the cable select with the older drive on a 40-wire cable, you'll have to consult the maker of the drive for the instructions. My sources tell me that there was a loose standard to put the Master drive on the end of the 40-wire cable and the Slave in the middle but that was a very loose standard. Makers I spoke to (IBM, Maxtor, etc.) informed me that the user should set the drive using the Master and Slave jumpers on the hard drive, placing the Master in the middle and the Slave on the end. Dats Dat.

80-wire Cables
On the ATA66/100/133 standard 80-wire cable, the Master hard drive or your boot hard drive goes on the END of the cable. This is true whether or not you use the Master/Slave style or the Cable Select style.


Frequently Asked Questions:

Can I connect a older ATA33 drive with my newer ATA66/100/133 drive?
Yes. But, you'll suffer a dramatic speed hit. Because of the slower drives controller, the PC will accommodate both drives by slowing down the pair to the older drives speed. Put your older drive on the Secondary channel with your CDROM as the Master.

What position should I connect my CDROM Burner if I want to put it on the 40-wire cable?
It should be the Master, and the hard drive (if you have one) Slave.

Can I put my brand new CDROM Burner on the Slave position on my 80-wire cable?
I wouldn't. That would slow down the hard drive.

Why does my motherboard detect my ATA100 hard drive as a ATA33 or DMA mode 2?
Some hard drives need to have a special driver that was supplied by the manufacturer to turn-on the ATA66, 100 or 133 feature.




The standard 40-wire ATA ribbon cable and the 80-wire cable give different drive behavior when using Cable Select. If using the standard 40-wire cable, the Master goes in the middle connector and the Slave goes in the end connector. If using the 80-wire cable, attach the blue end connector to the system board or host controller, the gray middle connector to the Slave, and the black end connector to the Master.

All newer IDE/EIDE hard drives can be jumpered as Cable Select (CS or CSEL). This is an alternate way to indicate which drive is master and which drive is slave (instead of jumpering one drive as master and one drive as slave). Cable Select jumpering requires a special IDE cable with wire 28 not connected to one of the drive connectors, which would configure the drive attached to that connector as the slave drive.

Cable Select jumpering is not widely used now, but may become more common as things move more towards Plug and Play, as this is part of the ATA PnP standard and Microsoft's PC97 standard. The idea is that drives can be installed easily without having to change jumpers on two drives anytime a drive is installed or removed. Cable Select is defined in the ATA-2 and ATA-3 specifications.

In order to use Cable Select jumpering, several conditions must be met. Both drives on a channel must support CSEL, both drives must be jumpered as CSEL, a CSEL cable must be used, and the host interface connector must support CSEL. For the host interface to support Cable Select, wire 28 must be grounded.

Although the Cable Select specification may simplify things in the future, there will probably be lots of confusion, especially on legacy systems, as this starts to be introduced. One problem will be in selecting the correct cable. Supposedly, the cables used for Cable Select will be clearly marked, with each connector labeled as Device 0 (or Master) or Device 1 (or Slave). If not clearly marked, it may not be easy to identify a CSEL cable visually. wire 28 can be checked for continuity.

A Cable Select cable can be constructed in various ways. Pin 28 may be non connected to the connector at the end of the cable or to the connector in the middle of the cable. Another design would have the host interface connector in the middle and the two drives would plug into each end of the cable, with the connector at one of the ends not connected to pin 28.

If both drives are set for CSEL and the host interface supports CSEL, but a regular cable is used, both drives will be seen as master.

A Cable Select cable can be used with master/slave drive jumpering.

Another problem will be with host interfaces on legacy motherboards and controller cards. If pin 28 is not grounded on the host interface, drives connected to either connector on the CSEL cable will be seen as slave. It will be common to find that pin 28 is open or high on many older IDE interfaces. This can be checked with a voltmeter.

Installing the 80-Conductor IDE Cable
The 40-pin 80-conductor cable is orientation specific. The cable connectors are color-coded: blue for the host connector, black and gray for the primary and secondary disk drives. The blue connector should be installed into the Primary IDE connector.

All Ultra ATA/66 devices should be attached to a single channel and devices that do not support Ultra ATA/66 should be connected to a separate channel. In single drive configurations, connect the primary drive to the end connector on the 40-pin 80-conductor cable.


From the horses mouth

Here are some quotes from leading websites about connecting IDE devices:

Intel - Installing the 80-Conductor IDE Cable
The 40-pin 80-conductor cable is orientation specific. The cable connectors are color-coded: blue for the host connector, black and gray for the primary and secondary disk drives. The blue connector should be installed into the Primary IDE connector.

All Ultra ATA/66 devices should be attached to a single channel and devices that do not support Ultra ATA/66 should be connected to a separate channel. In single drive configurations, connect the primary drive to the end connector on the 40-pin 80-conductor cable.

HowStuffWorks - How IDE Controllers Works
IDE devices use a ribbon cable to connect to each other. Ribbon cables have all of the wires laid flat next to each other instead of bunched or wrapped together in a bundle. IDE ribbon cables have either 40 or 80 wires. There is a connector at each end of the cable and another one about two-thirds of the distance from the motherboard connector. This cable cannot exceed 18 inches in total length (12 inches from first to second connector, and six inches from second to third) to maintain signal integrity.

The three connectors are typically different colors and attach to specific items:

The blue connector attaches to the motherboard.

The black connector attaches to the primary, or master, drive.

The gray connector attaches to the secondary, or slave, drive.

Along one side of the cable is a stripe. This stripe tells you that the wire on that side is attached to Pin 1 of each connector. Wire 20 is not connected to anything. In fact, there is no pin at that position. This position is used to ensure that the cable is attached to the drive in the correct position. Another way that manufacturers use to make sure that the cable is not reversed is by using a cable key. The cable key is a small plastic square on top of the connector on the ribbon cable that fits into a notch on the connector of the device. This allows the cable to attach in only one position

Computer Architecture at the institution of Computer Science at Umeå University in northern Sweden - Cabling for ATA
It's easy to describe the different cable types used by the ATA interface today because there really is only one standard. And that is a 40/80 PIN flat cable with 3 IDC connectors. You can attach up to two units on the cable, one master and one slave. The 80 pin cable is for use with Ultra DMA devices but the 40 pin cable can be used with newer Ultra DMA devices but no faster modes than Ultra DMA/33 are available in that case.

In latter years a new cable have emerged and that is a 44 pin flat cable which is mostly used for 2.5" internal hard drives. The 4 extra pins are used for supplying power to the drive. As far as we know there does not exist any external IDE cables.

Future for ATA
In order for the ATA interface to cope with the increased data clock rate in the future, a proper terminator has to be applied to prevent "ringing" in the cable. This is not easily solved while achieving backward compatibility and will require cooperation between the major hardware manufacturers to make it work. Perhaps a solution is around the corner as there is a draft for a FireWire ATA interface.

Maxtor/Quantum Serial ATA White Paper



 More Resources

IBM Drive Support

Longer 80wire cables?