In order to install an expansion card, you must stick it into one of those slots on your motherboard. There are different types of slots, although only a few are still used today. Let’s look them over.

• Industry Standard Architecture (ISA):
  This type of slot is the oldest still in use today. If you open up an old 286, you’ll see a few of these. An 8-bit ISA slot is capable of 0.625MB/sec transfer rate between the card and the motherboard. Later versions of this slot were 16-bit, capable of 2MB/sec. This is still slow compared to today’s standards, but cards such as modems do not require anything faster than this. If you look at your motherboard’s slots, the longer black ones are the ISAs. If they are all one size, they are all ISAs. Modern boards are not boasting any more than maybe two of these bad-boys, only because people only use them for their modems or older cards that haven’t yet replaced. Some boards no longer have any ISA slots, moving completely to PCI.
  
• Enhanced Industry Standard Architecture (EISA):
  This type of slot is not used very often in desktop machines. It is used mainly in servers, or computers that host networks. With such a computer, the demands placed on its components are too big for ISA to handle. Also, the EISA bus is capable of bus mastering, which allows components attached to the bus to talk to each other without bothering the CPU. This feature is much like SCSI and speeds up the computer quite well. Like ISA, this slot has all but gone the way of the dodo.
  
• Micro Channel Architecture (MCA):
  Not too common either, this bus was created by IBM. It is 32-bit, like EISA, but you can’t stick ISA cards into it. MCA was capable of bus mastering, plus it could look at other devices plugged into it and identify them, leading to automatic configuration. MCA also produced less electrical interference, reducing errors. MCA is history. Don’t get it. Nobody uses it.
  
• Video Electronics Standard Association (VESA):
  This used to be considered a very fast interface made up mainly for video cards of the time that demanded a little more bandwidth. The VESA-Local Bus, or VL-Bus, is connected straight to the CPU’s own internal bus, hence the name “local”. This bus can transfer data at 132MB/sec. VESA buses were basically an ISA slot with an extra slot on the end. The whole thing is about 4 inches longer than an ISA slot. Again, you don’t see these much anymore. This was pre-AGP, for sure.
  
• Peripheral Component Interconnect (PCI):
  PCI was developed by Intel, like the VL-Bus. It is different than the VL-Bus except that it runs at the same speed. There is a fast interface unit between the card and the CPU that does the talking. This unit made the bus independent of the CPU. The dependency was a drawback of the VL-Bus, which was limited to the 486. Also, you can plug cards into it without any configuring. The bus is self-configuring, leading to the plug-n-play concept in which each add-on card contains information about itself that the processor can use to automatically configure the card. This slot is most popular with Pentium and later machines, although occasionally you will see one on a 486. If you’re anything like me, you never have enough PCI slots.
  
• Personal Computer Memory Card International Association (PCMCIA):
  This is a special socket in which you can plug removable credit-card size devices. These circuit cards can contain extra memory, hard drives, modems, network adapters, sound cards, etc. Mostly, PCMCIA cards are used for laptops, but many PC vendors have added PCMCIA sockets to their desktop machines. The socket uses a 68 pin interface to connect to the motherboard or to the system’s expansion bus.
  There are three types of PC cards: Type 1 slots are 3.3mm thick and hold items such as RAM and flash memory. Type 1 slots are most often seen in palmtop machines or other handheld devices. Type 2 is 5mm thick and I/O capable. These are used for I/O devices such as modems and network adapters. Type 3 is 10.5mm thick and used mainly for add-on hard drives. When buying PC Card equipment, you must consider the size of the slot. In most cases, Type 3 can handle Type 2 and Type 1.
  
• Accelerated Graphics Port (AGP):
  AGP is a more recent bus technology designed specifically for graphics cards. The bus sits directly on the system frontside bus, giving it direct access to the CPU and the system memory. This means it is not hampered by the slower speeds of the PCI bus. Rather than discuss AGP all over again here, please check out this separate page on the AGP bus.

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