It depends on the form factor of the disk itself. If it's a 2.5" laptop hard disk that runs off of (E)IDE (about 40-44 pins you'll see when disconnected) then usually it will be powered straight from the IDE bus. If it's SATA or (E)IDE on any other form factor (SATA 2.5" laptop/3.5" desktop or IDE 3.5" desktop disks) then they'll need a dedicated 5/12V power supply that usually can be provided by a computer's power supply unit or via a special power brick (if you're using a SATA/IDE to USB interface).
A had drive receives it power from the power supply
It connects the drive to the system power supply.
An internal hard-drive fits into a bay inside the computer's tower. A power cable from the power unit is plugged into the hard-drive. A data cable plugs the hard-drive into the motherboard.
The Western Digital My Passport Elite external hard drive receives power through the USB connector. Some USB ports may not have enough power for the drive- this is very dependent on the PC or laptop. A USB Y power cable (readily available on eBay) will resolve the issue- it allows the drive to get power from two USB ports, one connector provides power and data and the other power only.
If the hard drive is moved to another system. The password will protect the hard drive.
Yes as long as the hard drive has its own power supply and not powered by the USB port.
Some of them do. Your CD-ROM and hard drive can have molex power connector, or/and SATA power connecter. I think SCSI interface uses molex power connectors too.
Because the moving parts inside a hard drive require power. Bigger hard drives require more power, so a large hard drive may need more power. USB external harddrives get their power from the computer via the USB ports, that is why some USB hard drive have 2 USB cables; both provide power to the drive and one transfers the data. This many not be enough for large hard drives so they need extenal power. (Just think, they could probably work off 4 or 5 USB ports, but most people don't have that many free!)
If you disconnect the power cord to the hard drive, when you turn the computer back on, the hard drive will not be operational. Additionally, if you leave the IDE (or SATA) cable connected when the power cable is disconnected, the system will take longer to POST because it will try to identify the device connected, but it will not be able to. If it is the only hard drive you have in your system, the computer won't boot up because your operating system is on the hard drive.
Commonly, external hard drives will acquire power from the computer it is connected to. It is possible, though, to connect external hard drives to an outlet and permanently to the computer, replacing the previous hard drive, though I highly do not recommend such.
The HDD, or hard disc drive is one example of a drive that does not require power to hold its stored data.
a flash drive No, not a flash drive....he is talking about the hibernate functionality
With hard disk reliabilities as good as they are, most likely no.