Multiple IDE devices on one controller

I know that having multiple IDE devices on one controller will cause the data to be transfered at the rate of the slowest device.

My question: Is the data transfer rate only affected when both devices on the controller are being used at the same time or is the data transfter rate affected even if the slower device is idle.

Scenario, two IDE hard drives, one IDE CD ROM.  Is it better to put the drives on separate controllers if the CD is used sparingly or should the IDE hard drives be on one controller and the CD on the other controller?
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slyskawaAsked:
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Will SzymkowskiSenior Solution ArchitectCommented:
You can setup the IDE chain so that the CD-ROM and HHD are sharing it. If you can work around this issue like putting CD-ROM on its own IDE cable this would be preferred.

You will also experience the HHD being slow if you do have the IDE Hard Drive and the Optical drive sharing the same chain.

Hope this helps.
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CallandorCommented:
>My question: Is the data transfer rate only affected when both devices on the controller are being used at the same time or is the data transfter rate affected even if the slower device is idle.

If a hard drive and a CDROM share an IDE cable, the hard drive should be ok as long as the CDROM is not being accessed.

>Scenario, two IDE hard drives, one IDE CD ROM.  Is it better to put the drives on separate controllers if the CD is used sparingly or should the IDE hard drives be on one controller and the CD on the other controller?

Since hard drives have better performance if they have their own controller, this is the preferable configuration if doing disk-to-disk operations.  Accessing the CDROM should be kept to a minimum.
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Gary CaseRetiredCommented:
Callandor's correct, but with an important caveat:   Many systems are shipped with an 80-wire cable on the primary IDE channel and a 40-wire cable on the secondary IDE channel.   Typically the primary channel is used for hard disks, and the secondary is used for optical drives.   Since optical drives generally transfer data at UDMA-2 rates, the 40-wire cable is fine.   IF, however, you're going to put a hard drive on that channel, you should be sure you're using an 80-wire cable.   Otherwise the maximum transfer rate will be UDMA-2 even if the hard drive is the only device on the cable.  (if the controller does not detect an 80-wire cable transfers will be limited to UDMA-2)

The BEST scenario is to always have every IDE device on its own channel.   I've found this to be an excellent and easy way to add additional IDE channels (and it's 48-bit LBA compliant):
http://www.newegg.com/Product/Product.asp?Item=N82E16816102007
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Gary CaseRetiredCommented:
... in case you didn't know the transfer rates, UDMA-2 is 33mb/s.   Typical hard disks will transfer at UDMA-5 (100mb/s) or UDMA-6 (133mb/s).   So you clearly don't want to use the wrong cable and restrict your transfers to the slower rate.
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