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Hard drives, IDE/ATA, whats all this "master" and "slave" stuff?

Hard Drive Cables Instructions:

"IDE" or maybe more properly "ATA" controllers are built into darn well every PC motherboard built in the last 8-10 years or so. Macs have been throwing them into many of their computers in the last several years as well. IDE is the predominate PC hard drive type, due to several factors, mostly involving price, which is for the most part due to the extreme volume of sales. Huh? Ok, don't get confused yet, there's more to come. There have been, for the most part, two hard drive formats of any value for the last decade. These are IDE (ATA) or SCSI (Supergeeks: please don't email about scsi being technically ata.... you know what I mean). SCSI (pronounced "scuzzy") has always been the choice of performance based computers (interestingly Macs were generally scsi) like servers rather than your basic PC desktop. There were, of course, PC's which were scsi based, but let's not get sidetracked into some weird mac/pc debate here. If your connector has 40 little holes in it, it's IDE, any more and it's SCSI, period. If it has "pins" instead of holes, it's a "Wide" scsi.
Allright, enough of the stupid scsi/ide discussion, you want to know the deal with this whole IDE thing. A typical IDE controller has two "channels". Each "channel" has one connector on the system motherboard or in some cases a seperate card plugged into the motherboard. If you don't know what the "motherboard" is, it's the biggest flat, board with all kinds of componants stuck on it, and cables going to it, in your computer. Everythings connected to it. So, most computers when they're new have one IDE cable which goes from the motherboard to the hard drive and cdrom drive. Sometimes they will connect them on the different "channels" which would mean that there would be two cables going to two connectors on the motherboard, one to the hard drive, one to the cdrom drive. It's important to note that each IDE channel will support two drives or less, giving you a maximum of four drives per IDE or ATA controller. You need more, you better add another IDE controller. Each channel will use an IRQ and I/O address as well, eating up valuable system resources, so an IDE based system must be planned to keep these limitations in mind. Another limitation is in cable lengths. The specs for IDE cables set the limit for length at 18 inches. This spec is for the newer ATA66 drives and controllers too, but don't shoot yourself if you "must" have longer cables, as engineers are quite careful types who don't get out often, and are rather opposed to experimentation. It may not be advisable, but 36 inch length cables are available and may, in fact work, but it may be a wise move to restrict any IDE/ATA cables to something a bit closer to the "official" spec, like, say, 24 inches if you value your data. If you really really value your data, stick with 18 inches, or less, or use the abovementioned "scsi" instead.

Masters/Slaves?!
The master drive is the "first" (as far as your BIOS is concerned, not the "first physical drive on the cable) drive on a channel of two possible drives on the channel. The first channel is usually assigned IRQ 14, the second channel IRQ 15. Huh? Don't worry about it, unless you want to have more than four IDE devices, total, including hard drives, cdroms, internal zip drives, etc. If you want to add an additional controller, you will need to find some IRQ's. Some of the newer PCI stuff is very happy to share "IRQ's" though, and then again, much of them are not. Four. That's the number. Remember it or get scsi stuff and scsi's associated nightmares. The first drive of the first channel is the "primary" drive. It will be the drive your computer will "boot" or start from. "Slave" drives are just as good as masters in reality but care must be taken when mixing and matching hard drives and cdroms (especially cdrw drives) on master/slave primary/secondary controller channels. It's probably best, in a two cdrom, two hard drive system, to keep the hard drives as masters on seperate channels, and the cdroms (cdrw's) on slave seperate channels. Then again, sometimes not, it depends on how you use the drives. The most used drives should be on seperate channels. Whith CDRW's you should keep the cdrw on a seperate channel from the hard drive it would read from. next......
Setting DMA mode for maximum performance.

IBM has a great page explaining the different Interfaces!

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