IDE and EIDE cable compatibility


Apr 10, 2000
I have a pair of single device blue rounded 40 wire IDE cables in my Slot A folding machine. Don't remember where I got them.:D


[H]ard|DCer of the Month - April 2010
Oct 18, 2001
The only difference between 80-wire EIDE cables and 40-wire IDE cables is that the former have 40 extra wires used for reducing crosstalk between the other wires. Those extra wires further do not prevent it from being used with an IDE device. The worst thing which could happen is that performance improves.

Ice Czar

i don't want to go off on a rant....but

the standard is fully backwards compatible (so technically your fine)
thats not the same as saying there will be no issues
the optical drives will certainly benefit from having the extra shielding from an 80 wire (the "new" 40 wires sharing a common ground to reduce cross talk) however, poorly made rounded cables leave alot to be desired, and there is definately a reason why SATA is being adopted, ATA\IDE\EIDE\ATAPI is an unterminated standard and as sppeds increase that causes more and more problems, especially if cheap cables are employed, complex device configurations, and poor cable routing

a few :)p) links and excerpts:
Standard (40-Conductor) IDE/ATA Cables

In many ways, the cable is the weak link in the IDE/ATA interface. It was originally designed for very slow hard disks that transferred less than 5 MB/s, not the high-speed devices of today. Flat ribbon cables have no insulation or protection from electromagnetic interference. Of course, these are reasons why the 80-conductor cable was developed for Ultra DMA. However, even with slower transfer modes there are limitations on how the cable can be used.

The main issue is the length of the cable. The longer the cable, the more the chance of data corruption due to interference on the cable and uneven signal propagation, and therefore, it is often recommended that the cable be kept as short as possible. According to the ATA standards, the official maximum length is 18 inches, but if you suspect problems with your hard disk you may find that a shorter cable will eliminate them. Sometimes moving where the disks are physically installed in the system case will let you use a shorter cable

Warning: There are companies that sell 24" and even 36" IDE cables. They are not recommended because they can lead to data corruption and other problems. Many people use these with success, but many people do a lot of things they shouldn't and get away with it. :^)

Ultra DMA (80-Conductor) IDE/ATA Cables

There are a lot of issues and problems associated with the original 40-conductor IDE cable, due to its very old and not very robust design. Unterminated flat ribbon cables have never been all that great in terms of signal quality and dealing with reflections from the end of the cable. The warts of the old design were tolerable while signaling speeds on the IDE/ATA interface were relatively low, but as the speed of the interface continued to increase, the limitations of the cable were finally too great to be ignored.

that "upgrade happened at 66MB/s burst, we are now at the same speed as the PCI bus for burst rates 133MB/s

Fancy IDE leads - The Terrible Truth

The spec mandates such short cables for two reasons.

Reason one - practically all IDE cables are unshielded. There's nothing around the conductors but insulation. Electromagnetic radiation goes straight through insulation. So external interference from the rest of your computer's giblets can influence the signal on your IDE leads.

Unshielded cables act like antennas. Generally speaking, the longer you make 'em, the more energy they can pick up from their environment.

Reason two - IDE cables are unterminated. "Termination", in the electrical sense, is essential to provide "impedance matching", which in English is what you have to do to stop the signal from reflecting off the end of the cable like a wave that hits the end of a bathtub.

Electric current does not move instantaneously down a wire. It travels at nearly the speed of light, but when you've got thirty-three and a third million clock pulses per second - which is the speed of the IDE bus - even light in a vacuum only moves a hair under nine metres per clock pulse.

So if you're fooling around with, say, a double-the-rated-length 900mm IDE lead, there's an end-to-end signal delay in it of about a tenth of a clock pulse. The signals you want your drives and your motherboard to be able to hear will be significantly blurred by delayed reflections from each end of the cable.

Transfer your data at twice or three times the UDMA/33 speed - as UDMA/66 and 100 do - and reflected signals get more and more out of step with the real signal, and do it more and more harm.

Serial ATA and the 7 Deadly Sins of Parallel ATA
Critical Limiting Factors in Parallel Design
There are some fundamental differences between serial and parallel buses, more importantly, there are some critical limiting factors in the design and implementation of any parallel bus.

1. Non-Interlocked (source synchronous) clocking
2. 3.3 V high-low signaling with 5V legacy tolerance
3. Cabling constraints
4. Connector legacy
5. Termination
6. Command queuing
7. PCB Design

3. Cable Design Issues: Cross-Talk and Ground Bouncing vs.Ringing

Each signal propagating through a data line makes the data line act like the inductor of a transformer. That is, each voltage swing generates a dynamic electromagnetic field, that, depending on cable length and proximity will induce another signal in adjacent data lines. This cross-talk adds noise to data lines and can produce errors by generating false positives or negatives simply by induction of voltage swings in data lines.

Another problem with parallel pathways is the phenomenon of simultaneously switching outputs (SSO) noise. As we explained in detail in our reviews of the i845 and the SIS645 chipsets, SSO noise becomes really problematic if the majority of signals switch from high to low since this can induce ground bouncing. On the chipset level, workaround in form of dynamic bus inversion (DBI) is feasible, that is, instead of switching all bits, only the reference bit is switched simultaneously at the sender and receiver end which has the same net effect, namely, that the system does not see the reference switch but thinks that all other lines have switched. DBI, however requires an additional latency cycle and this is where the 40 ns clock cycle time starts to look really ugly.

ATA not so Frequently Asked Questions
Or: Why Ribbon Cables are unsuitable for RF transmission of data

The following article was written by snn47 to address some of the issues associated with standard ribbon cables and the use of e.g. removable drive racks as an attempt to share some insight into factors that can adversely affect the life or reliability of of desktop Hard Disk Drives. Specifically, issues like why some drives are working in some systems and not in others, the impact of cable routing and why is it that the drive manufacturers always recommend using their own cables (if supplied with the drive). (emphasis mine)

Any RF system has a limited tolerance for distortion of signals, which, in the worst case, can destroy some of the semiconductor components. While a certain amount of variation is part of any systems specification, one needs to remember that ATA was never intended to handle today's data rates. ATA or Advanced Technology Attachment started as the usual run of the mill or: "just a system at the lowest possible price point that will work most of the time without the need for huge financial investments". The problems started when the system was forced to handle higher and higher clock and data rates within the original design limitations. Keep in mind that the latest ATA-PI7 specifications allow data rates of 133 MB/sec, which is 44-times faster than the original ATA transfer of 3 MB/sec. This increase in speed makes it necessary to enforce minimum tolerances and detailed specifications to allow for the manufacturing of affordable systems with minimum compatibility problems.

these are just a few excerpts, I would highly advice that everyone give them a good read, there ARE good rounded ATA cables RD3XP Super Shielded
"RD3XP is made from ATA 100/133 High impedance flat cable cut into 8 layers of 10 cable wires, with a ground wire and signal wire alternatively, and folded in zigzag-piled so that each signal wire is surrounded by 4 ground wires."

but like their SCSI counterparts, they aint cheap, there are also high quality flat cables (you buy a $300 RAID card, and they dont ship you crappy PVC cables, they are either Teflon or Thermoplastic Olefin (TPO)

Up until a little while ago I would have said ant investment made in high quality cables was money well spent, however with the introduction of SATA, that doesnt necessarily hold true anymore
unless your dealing with critical data (in which case you should be running ECC RAM) or your actually experiencing problems

a further excerpt from ATA not so FAQs

Preliminary Conclusions and Possible Cure

Reasons for changes in the propagation impedance, cross-coupling between adjacent signal wires and signal-velocity from one setup to another are :

Impedance of the drive and controller in high/low signal level will be different for different models.
Reflection of signals that garble the pulse, due to incorrect termination impedance or impedance-inconsistencies from the controller to the drive meaning the Impedance from the controller and the drive(s) differ.

If there is a a second drive (connector present/connected) the impedance will fluctuate at this point.

A. Only one HDD per controller channel.

B. Use a cable with only 2 connectors.

-Signal delay will increase with the length of the flat-ribbon-cable propagation of the signals were intended for a max. flat-ribbon-cable length of 18" with ~ 5ns/m would be 2.3ns delay.

C. shorten the cable whenever possible.

D. If the case requires long cables consider mounting just the HDD closer to the connectors of the controller or consider exchanging the usual desktop case, for a 19" case. Mount the HDD just above or below the PCB-controller-connector to allow you to reduce the length of the flat-ribbon-cable to a few cm.

Flat-ribbon-cable with different isolation material (higher/lower eR) and change in the conductor diameter will change the ratio of (2D/d).

Are rounded cable used?
E. Try exchanging the cable against another type/brand of flat-ribbon-cable.

Is the flat-ribbon-cable at some point parallel to a conducting grounded surface?
F. Try a different routing of your flat-ribbon-cable away from a ground-plane,

Was the cable cut apart and/or rolled it to get a rounded cable?
G. Unroll it and try B., if cut apart then start with A.

Is the drive mounted in a removable drive rack?
H. Remove HDD from the drive-bay and start with A.

well so much for not going on a rant
And this isnt just my opinion, and Im not wrong :p

However you should checkout the section in Dansdata's "IDE Fancy Leads, the terrible truth" as to why with all this goin on,
for the most part, it still works anyway :p

Check out what your chipset has to sort out here
click on a picture to see an animated test
(note not all types of cables where employed, for instance there are no high quality TPO or teflon cables in this test)

like the Power Supply, cables are widely underated as a source of problems, and few ever spend any money on them for anything but "looks"

Ice Czar

Its what Im here for :D

dont let all that scare you off or rush you into spending alot of money on cables, next year or the year after its possible you wont have any PATA (IDE) cables left in your case, In my opinion its the single best reason to adopt SATA today.

(there being no substantial SATA performance gain currently)

and that really is more for HDDs than optical drives, but opticals on the same channel as the HDD does impact the signal quality

but for the vast majority of users it still works just fine, but Im seeing more and more configuration problems in those rare instances (Brand name HDD X doesnt want to play well with Brand Y ect)