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What is the difference between IDE and IDC

Posted on 2005-04-20
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I am trying to pick out a new hard drive and have been informed that I need IDE but most of the drives I look at are IDC, what is the difference?
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Question by:Keogh_b
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by:Callandor
ID: 13827970
You better post a link.  I never heard of IDC - the two common types are IDE and SATA, with SCSI also available, but expensive.
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by:Keogh_b
ID: 13828111
Here is the link http://www.dabs.com/uk/channels/hardware/storage/productView.htm?quicklinx=2J7Z
and the spec reads

Dimensions & Weight / Depth  14.7 cm  
Dimensions & Weight / Height  2.6 cm  
Dimensions & Weight / Weight  0.6 kg  
Dimensions & Weight / Width  10.2 cm  
Header / Compatibility  Mac  
Header / Compatibility  PC  
Header / Manufacturer  Western Digital  
Header / Model  WD1600JB Special Edition  
Header / Packaged Quantity  1  
Header / Product Line  Western Digital Caviar  
Service & Support / Type  3 years warranty  
Storage / Type  Hard drive  
Storage Controller (2nd) / Type  None  
Storage Hard Drive / Average Seek Time  8.9 ms  
Storage Hard Drive / Buffer Size  8 MB  
Storage Hard Drive / Capacity  160 GB  
Storage Hard Drive / Connector  40 PIN IDC  
Storage Hard Drive / Data Transfer Rate  100 MBps  
Storage Hard Drive / Form Factor  3.5" x 1/3H  
Storage Hard Drive / Hard Drive Type  Internal hard drive  
Storage Hard Drive / Interface Type  ATA-100  
Storage Hard Drive / Spindle Speed  7200 rpm  
Item Value
Device Type  Hard drive - internal  
Width  10.2 cm  
Depth  14.7 cm  
Height  2.6 cm  
Weight  0.6 kg  
Compatibility  PC, Mac  
Form Factor  3.5" x 1/3H  
Capacity  160 GB  
Interface Type  ATA-100  
Connector  40 PIN IDC  
Buffer Size  8 MB  
Features  Data Lifeguard, Shock Guard  
Compliant Standards  S.M.A.R.T.  
Drive Transfer Rate  100 MBps (external)  
Seek Time  8.9 ms (average) / 21 ms (max)  
Track-to-Track Seek Time  2 ms  
Average Latency  4.2 ms  
Spindle Speed  7200 rpm  
Non-Recoverable Errors  1 per 10^14  
Start / Stop Cycles  50,000  
Interfaces  1 x ATA-100 - 40 PIN IDC  !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Compatible Bays  1 x internal - 3.5" x 1/3H  
Service & Support  3 years warranty  
Service & Support Details  Limited warranty - 3 years  
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by:fixnix
ID: 13828208
IDC is what the connector is called.... "40 Pin IDC" is the style of connector for IDE drives.
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by:Keogh_b
ID: 13828252
How can I tell the difference between a A 40-pin, 80-conductor IDE cable and a A 40-pin, 40-conductor IDE cable?
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by:fixnix
ID: 13828343
80-conductor IDE cables still use IDC 40-pin connectors, so the only way to tell the difference is to look at the "ribbon" part of the cable.

Obviously 80-conductor cables have 80 strands making up the ribbon and 40-conductor cables have 40.  If you hold two side by side the difference is visually apparent.  Once you've seen enough of them, you can tell just by seeing one cable by itself.  If you haven't seen enough to tell the difference, then I don't' know any other way than counting the strands making up the ribbon....count to 20 and if you're closer to 1/4 way accross the ribbon than 1/2 way then it's an 80-conductor ribbon.
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by:fixnix
ID: 13828371
you can attempt to count by sticking a fingernail in the little ridge between 2 strands, then gently and slowly take your fingernail accross the cable...counting the "humps and ridges"
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by:fixnix
ID: 13828399
For further reference, 80-conductor cables are necessary for reliable IDE operation at or above speed modes of ATA-66.  Slower drives will work at their designed speed with either 40 or 80 conductor cables.  ATA-66 and above drives *can* work on 40 conductor cables, but their speed mode of operation should be reduced to ATA-33 or Mode-4 or slower to reduce the risk of data corruption (might even happen automatically...not sure on that one)
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by:Callandor
ID: 13828430
I think most 80-conductor cables have a black connector for the motherboard side and a blue connector for the drive side.  The 80-conductor cable provides better shielding for each signal wire.
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by:fixnix
ID: 13828555
Callandor:  Good point.  I know I have plain ole black/black/black IDC 40 and black/black/black IDC 80 conductor cables laying around, but as far as I remember, every black/blue/blue cable I've seen has in fact been an 80-conductor one.  It's not necessarily a 100% accurate indicator, but probably accurate enough most of the time.
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by:Watzman
ID: 13828639

IDC is "Insulation displacement connector".  It refers to ANY connector that makes it's contact with the wire by "piercing" the rubber insulation of the wire or cable with sharp blades.  Most of the connectors used for disk drives which have an IDE interface are IDC connectors, but there are all kinds of IDC connectors, for example 25-pin printer port and both 9-pin and 25-pin serial port IDC connectors are available.  IDC doesn't tell you what the connector is for, only how the connector is attached to the cable.  The alternative is connectors that you have to strip each conductor and individually solder it to the connector pins.

[by the way, IDE stands for "Integrated Drive Electronics" and means a drive that has the controller in the drive itself.  The controller on the motherboard is just an interface, and not really a "true" disk controller that deals with things like data separation, encoding and precompensation.]

You can tell the difference between a 40 and an 80 conductor IDE cable by counting.  You don't have to count all of the wires, and you don't have to be exact.  Since the cable is either 40 conductors or 80 conductors, just start counting about one-quarter of the width, and you will be "close to" 10 or 20, and that's enough to tell you if it's a 40 or 80 conductor cable.  Note that both 40 and 80 conductor cables use 40 pin connectors.  On the 80 conductor cables, every other conductor is a ground, and that connection is made inside the connector.  Also, on 80 conductor cables, the 3 connectors (motherboard, master and slave) are different (there are some connections made inside the connector itself that are not the same), so you cannot interchange them.
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by:fixnix
ID: 13828933
Watz:

Are you certain about "Also, on 80 conductor cables, the 3 connectors (motherboard, master and slave) are different (there are some connections made inside the connector itself that are not the same), so you cannot interchange them."?  Specifically not being able to interchange them?  I know for certain I've used them on the "wrong" devices many times without problems...probably have a couple mismatched cables in running machines at home right now.  One I'm nearly 100% positive that it has an ATA-66 hd on the same cable as an old 16x or so CD (which certainly did not require an 80 conductor cable).

I'd be interested in seeing a link showing the differences...maybe the machines I've slapped the wrong cables in are just generating higher than normal CRC errors yet being corrected by the IDE devices.  I wouldn't notice the performance hit because the "slapped together" boxes don't do much besides crunch seti units or occasionally get temporary shell or httpd duty when I need something expendable and isolated from the "real" boxes.
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by:fixnix
ID: 13828946
(and good info on what IDC actually is, btw....I assumed it only referred to the IDE connector from the brief searching I did.  Good work :))
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by:Watzman
ID: 13828995
Re: "Are you certain about "Also, on 80 conductor cables, the 3 connectors (motherboard, master and slave) are different (there are some connections made inside the connector itself that are not the same), so you cannot interchange them."? "

Yes, there are some pins connected together inside the connectors, and they are not the same pins in all 3 connectors.  If you are willing to take a cable apart, you may be able to see this (I have done this), but sometimes the connection is on top, where the blades pierce the cable, and it's visible, other times it's down in the body of the connector and not visible unless you really take it apart (e.g. break it).

It may be that this only comes into play for cable select drives (vs. explicit master slave selection), or vice versa.  I noted the pins connected together inside the connector, but didn't bother to trace out which pins they went to.  It is one of those "in the connector" connections that enables the controller to know if you have a 40-pin or an 80-pin cable.  Also, the 3 different connectors are color coded, blue, gray and black, as someone else noted earlier.

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fixnix earned 2000 total points
ID: 13829269
Ahh, thanks for the info Watz.  It probably is a cable-select thing because I do remember having an HP set to use cable select and I had problems swapping drives and cables in that machine.  </fog clears> :)
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by:Watzman
ID: 13829593

Cable select requires a modified cable even for 40-pin cables, so some of what I saw may have been related to that (although the modification is an open in one of the lines, not a short)
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by:MrPete_
ID: 13898961
Watzman's "only one way" information is truly only for a cable select cable, and in all my years I've only seen a very few, and not since 2000! (Except for floppy drive cables which normally have a very visible "flip" in them.)

It's quite easy to distinguish 80 and 40 pin cables without counting. Grab a floppy drive cable -- the cable is quite "bumpy" and looks exactly like a 40 pin IDE cable except a bit narrower (36 pins). An 80 pin IDE cable has VERY fine wires by comparison... almost smooth.

Any ATA/IDE drive purchased in recent years typically comes with the proper 80 pin cable... and it absolutely CAN be used "swapped around". Not that you would usually do so, since you usually want to have those two connectors available for a couple of drives.

The whole thing is actually amazingly simple. To clear up the confusion a bit, here are the pieces worth knowing:

1) What's the overall drive called?
2) What's the electrical/command interface?
3) What cable is needed?
(There's more but you really don't need to worry about it)

There are three common types overall:
    * "IDE" is the most common. Connectors/cables are 40/80 pin. Interface is ATA-nn (nn can be 33, 66, 100, etc) or on older ones, just IDE.
    * SATA (Serial ATA) is newest. A small connector is used. Interface is also called SATA.
    * SCSI is used in high performance systems. Expensive in every way, but fast especially w/ multiple drives in a server. Cables are all quite different from IDE or SATA

With ATA/IDE drives, the only other thing you really need to know is about master/slave configuration. That's done by moving a little pin around on the drive itself. Usually near where the cable attaches, and usually there are instructions on the drive label.
Normally, there's one setting for a single drive by itself, which also makes the drive the "master" (first drive) when there are two on the cable.
And then there's another setting for the "slave" (second drive) when there are two.
...and it doesn't matter where on the cable you put the two drives. That jumper determines which is #1 and which is #2.

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by:MrPete_
ID: 13898980
Basically, I tell people to use IDE/ATA drives. SCSI is for expensive servers. SATA is new and exotic and still often both expensive and tricky to find parts for.

Obviously, don't let yourself get confused between ATA and SATA!  SATA is **not** what you want. ATA and IDE are basically interchangeable terms for the same drive (ATA is the "electronic interface" while IDE is just the traditional term for the drive overall.

(Once upon a time, drives had to have fancy external controllers... until we Integrated the Drive Electronics into the drive... hence IDE. Yeah, I used to work on such things...)

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by:Watzman
ID: 13899405
Floppy cable has 34 pins, not 36.  But you are right, if the hard drive and floppy cable are the same "fineness", it's 40 pin, if the hard drive cable if much finer (exaclty twice as fine), it's 80 conductor.

Most of the large OEMs (including Dell, from the ones I've seen) are now using cable select.  They do it for their benefit, a system may have from one to four IDE devices, and that way, they don't have to set any jumpers at all, just slap the drives into the machine.

However, I still take issue with Mr. Pete that you can swap the connectors on an 80 conductor cable. I've built the cables, and taken some apart, and the connectors have connections inside them, and they are different.  Some of these connections account for the ability of the controller to detect a 40 vs. and 80 conductor cable.  But when I've tried to swap them, also, it simply has not worked.
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by:MrPete_
ID: 13899511
> Floppy cable has 34 pins, not 36.
Oops. Sorry, a typo. :) [I had even counted to be sure!]

>I still take issue with Mr. Pete that you can swap the connectors on an 80 conductor cable. I've built the cables, and taken some apart, and the connectors have connections inside them, and they are different.  Some of these connections account for the ability of the controller to detect a 40 vs. and 80 conductor cable.  But when I've tried to swap them, also, it simply has not worked.

You may have had some other issues then, because electrically they are the same and there are no components involved.
If you were trying to use TWO drives, then it probably would not work. Also, if you were trying to use just the two "drive" connectors, that also would not work.
Put simply, for connectors C (computer), S (slave) and M (master), you can swap C and M as you like, **as long as only one drive is in use**. The M-S connection may not be detected as an 80 pin cable.

Most people probably are already bored :)... but if you really want details and backing documentation, read on.

Here's the facts:
* There's NO difference in signals on 40 and 80 conductor cables.
* Cable Select (CS - pin 28) is simply not connected to a connector that defaults to be the Slave. On a 40-cable, that's the end-drive, on 80-cond cable, it's the middle drive.
* 40/80 conductor detection is through the PDIAG signal on pin 34. The conductor goes through on 40-cables, but is broken on 80-cables. Drives pull the signal up, controllers pull it down. Thus, on a 40-cond cable, the controller can see the "high" level on the cable, while on an 80-cond cable, the controller will see "low".
* ALL 80-conductor cables must support CS; the gray connector is the slave.
On the "can you swap around" question:
* There is no difference between the "computer" end and the "master" connector.
* If you use CS, then you can't plug the gray connector into your computer. Not that you'd want to.
* If you use two drives, then you must use the cable as indicated.

A good not-too-tech resource with photos is http://www.pcguide.com/ref/hdd/if/ide/conf_Cable80.htm, while Intel's IDE chip spec is detailed and authoritative (http://www.intel.com/design/chipsets/designex/29065701.pdf)
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by:fixnix
ID: 13899553
wow....this thread is still going?  and just when I thought all that could be said about the cables was already said ;)  wondering what other takes will surface next week!


Good info tho.  Y'all answered questions I didn't even know I had ;)
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by:MrPete_
ID: 13945209
Keogh_b, sounds like you're putting together a nice computer here :)... have you had a chance to make progress yet?

An encouragement:

It's actually quite difficult to seriously mess things up, as long as you mount the m'board properly in the case (get that wrong and you can short stuff out pretty easily.)

Just about everything else that matters (i.e. could burn out) only goes in one way!

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by:rindi
ID: 14814716
Keogh_b,

No comment has been added to this question in more than 21 days, so it is now classified as abandoned..
I will leave the following recommendation for this question in the Cleanup topic area:
Accept: fixnix

Any objections should be posted here in the next 4 days. After that time, the question will be closed.


Rindi
EE Cleanup Volunteer
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