Yes, you can have as many as your case and motherboard will support.
yes we can plug more than one
yes
yes! A single portable hard drive can be used to back up more than one computer. but don't forget that which backup file is of which computer
An internal hard drive will generally be faster than an external one.
Each disk partition, regardless of whether there are more than one physical drives in the system, is given a drive letter.
Most laptops are simply not large enough to hold more than one hard drive internally. Supposing that one did, yes, it is quite possible to have both an SSD and a traditional hard drive in it.
Hard Drive configuration is used to define the Slave and master Hard Drive. When we are attaching more than one hard drive the configuration is used. Configuration is done by jumper setting which is available in back side of hard drive...1st two pins for master hard drive and last pins are slave..
As much as you need to store your files. More than one, less than a terrabyte.
Generally speaking, hard drive cases do not offer more protection than another case. If you drop a hard drive while in its case, the resulting shock may displace some of the hard disk platters which will ultimately prevent the disk from being read. Additionally, a fully enclosed hard drive case is not healthy for the hard drive if the case does not provide a way for the hard drive to radiate heat. Please note that hard drives are one of the hottest (temperature wise) devices running in your computer. The friction caused by a spinning hard drive is what generates the heat in a hard drive so you must ensure that the hard drive has proper cooling available to it.
In general, there is no reason to have more than one partition on an external hard drive. There are some specific cases where it might be desirable but you would know if you had a requirement like that.
Certainly. Many (most?) modern hard drives have only one root directory. Only those drives with two or more partitions will have more than one root directory.
There may be more than one meaning, but Hard Drive Setup Utility seems the most likely.