On any IDE port (you're concerned with the Primary here) you MUST have a Master device, and you MAY have a Slave. Usually these are set by placing a jumper on the correct pin pair on the back edge of the unit, according to the diagram on the drive itself. So, do you have a Master drive already? And this Slave you speak of, is its jumper set to Slave?
Once the jumpers are set, you SHOULD plug the one set to Master into the END connector of the data cable, and the Slave into the middle connector. Of course, both drives will need power connections in addition.
The alternative is to set the jumpers on BOTH drive units to "CS" (Cable Select). Then the one plugged into the END will be the Master, and the middle one the Slave. BUT you cannot mix the systems - either set Master and Slave, OR set BOTH to CS.
This may be the place to get an answer to my question.
I plugged in the HD's as follows: GSATA3 6 / GSATA3 7 / GSATA2 8 / GSATA2 9 on the mobo header. each drive has it's own sata cable. (GIGABYTE GA-X58A-UD3R LGA 1366 Intel X58 SATA 6Gb/s USB 3.0 ATX Intel Motherboard)
For some reason one of my hard drives is in 'slave' the other three are in 'master' . Their are no jumpers in any of them. Why is this and does it matter. I want to set these up in RAID 10 array.
You should know that this is my first build and I know as much about computers as I do about brain surgery.
Western Digital Caviar Black WD1002FAEX 1TB 7200 RPM SATA 6.0Gb/s 3.5" Internal Hard Drive. Three of this type and one is the same except it's a 3.0Gb/s
On some mobo's the BIOS assigns names like Master and Slave to SATA devices when there are really so such things as Master and Slave for any SATA! I don't quite know why they continue doing this. Just ignore that.
I'm not sure why you chose those particular SATA ports to use, but for many things that does not matter. HOWEVER, it may matter for your plan. It appears you have two connected to a SATA3 controller, and the other two on a SATA2 controller. Very often the built-in RAID systems only work on ONE controller, with all of the drives involved in the array connected to that same controller. So, read your manual carefully and check whether you need to connect all four to the same controller. The fact that you have three SATA3 (6 Gb/s) drives does NOT mean they have to be connected to a SATA3 controller.