Expansion Cards
Expansion cards "expand" the capabilities of your PC. They have ports on the back side, which allow other devices, called "peripherals" (monitor, speakers, phone lines, etc.) to be plugged in. They are called "cards" because of their shape and size - similar to a hallmark card - only thicker. Some refer to them as modules. The cards themselves are comprised of a circuit board and electronic components. They have a row of copper contacts along one edge - that edge is inserted into a slot on the motherboard. The cards plug into a series of side-by-side slots on the motherboard, and are positioned so that one edge faces the back of the PC. The slots are connected to a "bus", which in turn, runs along the bottom of the motherboard, and connects to the memory chips, and the CPU.
The "Expansion" Bus - "Expansion Card" Fiasco - (repeated paragraph from the Buses section) - in older PC's, the ISA bus was, and still is, called the "expansion bus", since it "expanded" the capabilities of the PC by allowing it to connect to peripherals. At that time, all the cards were ISA cards, and were given the name "expansion cards". Since the advent of newer, faster buses, such as the local bus (PCI) and the AGP bus, the cards, unfortunately - are all still called "expansion cards". This is unfortunate and confusing, since only the ISA cards are actually plugged into an expansion bus. They should have named all buses expansion buses, since they all perform that function - and simply differentiated the various types of expansion buses, but they didn't. So just keep in mind that there is only one expansion bus, the ISA bus, but the cards connected to the other buses are all called expansion cards. The extinct MCA and EISA buses are also expansion buses, just as ISA - but we will not discuss extinct architectures here.
There are three main flavors of cards, as shown above. You can always tell them apart by the slot connectors - not the components. We will discuss the cards and three bus types. There are a few older types of buses, such as EISA and VESA local bus - as well as some new buses that are forever in development, but ISA, PCI, and AGP are in 99% of today's PC's. The slower ISA type is being phased out, while new, faster versions of PCI and AGP are on the horizon.
There are many types of expansion cards, but we will only cover the standard ones here. Each card relies on software, called "drivers" - which allow Windows to communicate with the card. Each card in inserted into a "slot" on the motherboard, and each slot is connected to the main system memory, and the CPU with a number of electrical lines that run along the bottom of the motherboard, called a "bus".
The Slots
The type of slot is indicative of the type of bus that runs underneath the slot. All slots are mounted on the motherboard, perpendicular to the back of the PC, so that when you plug the cards in, a metal strip along the back side of the card, fits snugly against the back of the PC, and a single screw can be inserted to hold it in place.
The slots are hard plastic, with copper, tensioned receptacles lining either side. The cards actually fit very snugly, and they can be difficult to insert and remove. The retaining screw is required, however, since over time, the cards can work themselves loose.
Slots are color coded. Black slots are ISA, white slots are PCI, and brown slots are AGP. ISA and PCI can accept a huge variety of cards, while AGP is exclusively for video cards.
The old standard . . . ISA slots, are long, because they were made ages ago, when circuitry took up a lot of real estate. They are made to accept either 8-bit or 16-bit cards (the 8-bit ISA cards are short, and use up half of the slot, while the 16-bit ISA cards use the entire slot). The ISA card pictured above is an old, slow (28 kbps) 8-bit modem.
Inserting and Removing Cards - since the fit is very snug, inserting cards generally does take a bit of force. So much force, in some cases, that you may be worried about damaging the card or the slot. The trick in insertion, is to make sure you have lined the card up properly - if you force a card in, that is not properly lined up - you could damage it, although I have never seen this done. Place the edge of the card into the mouth of the slot, and make sure the metal edge is lined up. You will see that the metal extends downward about 1/2" - this tab must go into a small slot, or else the card will not move down far enough to insert it !! Rock the card slightly towards the back of the PC, and then the front (not side-to-side !!), and it should go a bit farther into the slot. Once you have a small amount of the card down into the slot, apply a firm, even pressure, and the card will literally "pop" down into the slot. Make sure to insert the mounting screw, once the card is inserted !!
To remove a card, take out the mounting screw, grasp the card firmly, and apply the same front-to-back rocking motion. It helps to initially grab the metal tab, and pul it up about 1/4 of an inch, and then grab the front end of the card (facing the fron of the PC) and pull that up 1/4 of an inch, and then repeat.