The connector was labeled "PRI IDE".
Does this mean that the device connected to it will be the primary drive?
It can mean two things.
First (and easiest) is that it is from the time where most motherboards had two IDE connectors on the motherboard. You could connect up to two devices per cable. Since only one device on the cable/bus could be active at the same time it was more efficient to put two harddisks on two different cables. Labeling them would be a nice touch. (But does not change anything. You could just use that cable on the secondary IDE port).
The second option is more likely but a lot longer to explain.
In the past the old setup was [Computer] [harddisk controller] [harddisk].
The harddisk controller was a separate and usually quite expensive card. That card interfaced with the computer (e.g. via the ISA bus in an IBM AT) and via cable(s) to the harddisks. (e.g. for MFM with 4 cable pairs. One to carry the analog data from the drive heads, one to control the disk).
Around that time some drives come on the market with the controller card integrated into the drive. We called it Integrated Drive Electronics. The connector on the drive was designed to directly interface with the AT bus, and another name for it was AT Attachement.
That controller was use to control a single drive an the setup would look like this:
[Computer with ISA ports]
|
[Connector card which was often called the HDD controller]
(it was merely a device which changed the small 40 pin cable to a ISA bus form)
|
[Harddisk with integrated harddisk controller]
If you wanted a second harddisk you could plug in another of these so called 'harddisk controllers'. That was a waste. Later versions changed this to allow up to two devices on the same cable. You needed to tell (jumper) each device to tell it about the other devices. The modes were:
- Single: Sole device on the cable.
- Master: There are two devices on the cable. Control yourself and take control of the other device.
- Slave: There is another device on the cable which will control you.
Setting the wrong mode would result in all sorts of trouble. E.g. If you have a single drive and set it to master it will (should) look for the slave and configure it. If there is no slave then it can keep looking forever. (Result: The disk hangs forever).
Later things got muddled because several manufacturers implemented smarted controls. As a result many drives use the same jumper setting for both "Master" and "single". Note that I said many, not all. Setting master mode on a single drive might thus work with one drive and fail with another.
A second 'helpful' addition is Cable select. The wiring on the IDE cable is used to determine if a drive needs to set itself to Master or to Slave. Those cable often have markings to indicate which one is the primary (aka master/single).
So much for the second option.
Will a third one slow down the system?
No. It will not slow down your other OS.
Whichever OS you install on the IDE drives might be a tad slower because those drives are older and most older hardware was slower than current hardware. It will not affect your other drives though.
Do I have enough power to supply the third HDD?
If you have about 20 Watts left on your current power supply unit: Yes.
For precise figures: Check the power usage of the current system and read the label of the new drive. It should state how much power it uses. On average that is about 25-30 Watt at spin-up and about 15 Watt afterward.
To answer your "Do I have enough power" question, we need to know the wattage of your power supply, and the power ratings for the existing drives. – Don Simon – 2013-02-21T15:55:47.917