Just like how people, cars, buildings, amongst other things take up space in the real world, it is the same with computers. The more complex things are, the more space they take up. Over time, the space gets used up. In the old days drives were not usually any bigger than a few gigabytes, but today's hard drives keep getting bigger and bigger. Everything has a capacity including hard drives and the more stuff that gets downloaded, installed, and used; eventually that drive will get full because everything takes up space no matter how big or small.
In the computer's HARD
The most common problem with large hard drives is computer crashes.
Assuming that when you say system unit of a computer you mean the computer case A.K.A. the tower, then no, hard drives are not always installed internally. Hard drives can be in external enclosures, hard drive docks, and even network attached devices.
The best place to visit about purchasing computer hard drives is an online website. A person can go on Amazon, Ebay, Newegg, or Bestbuy website to find the best place to visit about purchasing computer hard drives.
hard drives
The space inside the computer for DVD/CD/Floppy(who uses these anymore?) Drives and also Solid State Drives (SSD) and Hard Drives.
Depending on what computer you got but they are found inside the computer or tower.
Hard Drives, CDs, Floppy disks, USB drives.
the hard drives can be switched and what ever was on them will stay on them.
Internal Desktop refers to electronic computer parts that are designed to be installed inside a desktop computer. e.g Internal Desktop Hard Drives are hard drives designed to be installed inside a desktop computer.
This company sells used computer equipment. The equipment can include computers, networking equipment, computer components like hard drives and disc drives.
Yes, you can install multiple hard drives in your computer. If you have multiple internal bays then you can install drives inside the case. If not, you can buy external Firewire and USB drives that attach to the ports on the back of your computer. If you are unfamiliar with opening your computer, then choosing an external solution is the easiest and beth method.