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why is it recommended to use the furthest connector on a ide cable to connect a ide hdd?

Posted on 1998-08-31
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Last Modified: 2010-04-26
I have a aopen ap5t motherboard and it says in the manual that it is recommended to use the furthest end connector to connect your hard drive, but i used the middle one because im going to connect the furthest one with a internal zip drive.
why is it recommended to use the furthest connector?
does it have any effect?
would i have any future problems?
would their be any problems with the int zip drive?
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Question by:juggernaut
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by:mark2150
ID: 1124191
Are you talking cable or card slot?

In the bad old days some motherboards were made with a slot dependency in them. This has mostly passed.

If it's the cable connector you're referring to then it's for termination. You want to hang the drive on the end of the cable to keep the cable properly terminated. This will reduce EMI and ringing. If you connect a drive to the middle connector and leave the farend free then there will be an electrical "echo" from the unterminated end that will degrade the noise margins on the signals going to and from the drive. While this normally is not a major problem, it's good practice to keep your cables terminated to maintain signal integrity.

Yes, you could have problems in the future if you leave the cable unterminated by a drive. Since the IDE drive cables don't have a twist like the floppy cables, install on the end connector until you add your ZIP drive and then you can move things around to fit better. The ZIP drive will terminate the cable just as well as a HD will and as long as SOMETHING is plugged into the end connector, all should be well.

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by:juggernaut
ID: 1124192
so their wont be any problems using a internal zip for the terminator
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by:warmcat
ID: 1124193
mark,

1) The guy says ''connecting to his hard drive'', so he's not talking about slots

2) The IDE interface is *unterminated*  So the lecture about termination from SCSI 101 has probably frightened jug senseless.  Jug: ignore.

3) You missed the actual answer, which is that one of the IDE connectors on the motherboard is the Primary IDE interface and the other is the Secondary one.  If jug's setup is working with the HDD connected to the secondary interface, then he should stop worrying, but bear it in mind if he ever changes operating systems.  It is expected that your HDD is on the primary interface and setup as 'master', but if your BIOS and OS are happy with it as it is then it will cause you no problem.

Regards,

-Andy
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by:juggernaut
ID: 1124194
my hdd is setup on master on the first connector i think its called primary connector so would i have any problems also im going to install a internal zip drive to terminate
my basic question is would i have problems should i worry cause my hdd is on the primary connector and my hdd is setup as master?
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by:warmcat
ID: 1124195
Jug,

This stuff you've been hearing from Mark about termination on IDE is nonsense, and you should forget about it (and reject his answer accordingly).  Termination is a real issue for SCSI systems, not IDE.

Having your HDD on the primary IDE interface and setup as Master is *PERFECT*.  That's how 99% of machines out there are set up.

When you install your ZIP drive, set the ZIP drive as a slave IDE device, and try it on the same cable as your HDD initially.  If you have trouble there, swap it to being on the other cable.

Worrying is good, but this will probably 'just work'.

Regards,

-Andy
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by:plastic_74
ID: 1124196
Juggernaut,

Well I'm strongly support Andy's comment here......give it a try

Good luck :-)
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by:public
ID: 1124197
If the manual recommends using the other connector, you probably have your hdd on the second ide. Usually this works. IDE cables do not use termination, but should be less than 18" long. On some Hsing tech motherboards the total prim and sec length added should be less than 18", since only one set of buffers is used.
In most systems the boot hdd can even be a single slave without master on any channel.
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by:Otta
ID: 1124198
WARMCAT wrote:
> You missed the actual answer,
> which is that one of the IDE connectors on the motherboard
> is the Primary IDE interface and the other is the Secondary one.

I think that you missed the point that each of the two IDE
channels can connect to two IDE devices.
One device on a particular interface is labelled "master",
and the other is labelled "slave".

So, given an IDE cable with three connectors
(end, middle, other-end) and one IDE device,
should you connect the device to the "end" or the "middle" connector,
given that the "other-end" connects to the motherboard.
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by:MATTCEI
ID: 1124199
Mark2150's answer was correct.ALL electrical conductors are subject to signal degradation depending on where a resistive load is placed on them.Idealley,they should be placed at the very end.SCSI devices are just much more sensitive to this due to the type of line drivers used.With IDE,it usually makes no difference.You probably will see some 'ringing' or secondary 'ghost' waveforms if you look at the signals with a scope with the IDE cable continuing unterminated past the last device,but once again these are not strong enough to affect IDE devices.
SO - middle or end connector makes no difference PROBABLY - but why not do as he suggests and put the hard drive on the end for now,then move it to center when you add the ZIP drive?
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by:warmcat
ID: 1124200
Otto,

You're right.  On rereading jug's question, the ''two connectors'' he's talking about are clearly the two IDC sockets on the ribbon cable, not the two headers on the motherboard.  However...

MATTCEI,

Mark's answer, and yours, are incorrect with regard to termination.  A modern HCMOS input, such as is found on a HDD or CDROM, has an impedence of more than 10MOhms, which has as much terminating effect as a gnat farting ten feet from the PC.  IDE is designed to be unterminated (source: The SCSI Bus and IDE Interface, 1995, Freidhelm Schmidt, ISBN 0-201-42284-0) and so long as the mandated maximum cable length is not exceeded there will be no problems at all whatever the device ordering.

Maybe you'd like to educate me with more detail about ''the type of line drivers'' you mention used in SCSI adapaters, and how they differ from the buffers used to drive IDE cables, and your proposed mechanism for why they are ''much more sensitive''?

For a single peripheral on an IDE cable, using the middle or end connector ''makes no difference'', full-stop.

Regards,

-Andy
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mark2150 earned 10 total points
ID: 1124201
The free end of the stub cable *WILL* cause reflections. This *DOES* degrade your s/n ratio no matter if the *spec* says it's OK. The general advice of not tapping in the MIDDLE of a cable is good no matter what! Same concept applies at the PC trace level. Good electrical practice dictates that you don't leave an unterminated stub anywhere you have high speed signals. I wasn't quoting the spec, I'm quoting good electrical design. The original question is why is it " recommended to use the furthest end connector" and that is the reason. It's one of those suggestions that is good practice, and while it may not help much, it certainly won't hurt. The general concept is that you should apply conservative design rules *everywhere* to prevent noise and tolerances from stacking up against you. Yes, it won't make a huge difference (I did mention that) but the inside of a PC chassis is a very noisy environment and every little bit helps. Its like the advice not to fold ribbon cables all nice & neat.
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by:warmcat
ID: 1124202
Jug will have to decide what advice he takes away from this ''free and frank exchange of views'', but here is my version of the answers:

>why is it recommended to use the furthest connector?

It was recommended due to Mark's reasoning.

>does it have any effect?

No readily measureably effect at all, due to the high input impedence of the transceivers used on the peripheral.  The advice is redundant and you should ignore it.

>would i have any future problems?

No.

>would their be any problems with the int zip drive?

No.

Regards,

-Andy
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