What Are Expansion Cards And Slots?

Machines that have closed architectures are those manufactured in such away that user cannot get inside to add any new devices. Most computers have open architectures. They allow user to expand their systems. This permits users to insert optional device known as expansion card (also known as expansion boards or plug-in boards), which give the computer additional options.
Most motherboard in IBM-type computers has expansion slots. Expansion slots are socket on the motherboard into which expansion cards may be plugged. The slot connects the expansion card with the power supply and the buses for moving data and instruction. Among the kind of expansion cards available are the following.
         1.    Memory: Memory expansion cards (or SIMMs) containing additional RAM chips will give the user additional main memory.                                                                                                                                                                                          
2. Modem: A modem changes the electronic signal of the computer into the form that be sent over telephones lines. An internal modem is installed as an expansion card.
3. Video Display: Video display cards enable user to have better resolution or more colours on their monitor.
4. Sound: Circuit boards are available to gives computer sound output, if speakers and supporting software are available.
In order to make these expansions work it is necessary to follow software instructions provided with them.

Expansion cards are just like they sound, they are add-on cards that go into the computer to add or enhance what the computer can do. A couple of examples are a video card. This card could be added to computer that say doesn't receive or display TV signals, by adding  the card with that option, you would be able to feed a TV signal into it and watch TV on your computer screen. And a USB expansion card. This card would be used to add or add more USB connectors to your computer, without adding a HUB box to the computer. The slots are just the location, (usually on the mother or main board),  where the cards plug in. There are different types of slots depending on the age of the computer and also what the slots will let you do.
For example a video slot is where a video card would be installed, whereas a PCI slot could be used for adding most other cards.
Not to confuse you, but the PCI slots are most common, and one can even get video cards for the PCI slots. BUT you would not be able to install any other cards except a video card in a video slot. The video slot is made to directly access the computer memory for displaying what will be seen on the monitor.

Hope this helps you.

Take care.