EXPANSION CARD SLOTS

• Industry Standard Architecture (ISA) This is the most widely used bus, because it is the original. If you open up an old 286, you'll see a couple 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 bus were 16-bit, capable of 2MB/sec. This is still slow, but cards such as modems do not require anything faster than this. If you look at your motherboard's slots, the longer ones are the ISAs. If they are all one size, they are all ISAs.
• Enhanced Industry Standard Architecture (EISA) This type of bus 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.
• 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 is a very fast interface made up mainly for fast new video cards. All of those fancy videos and graphics require much speed. 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 are basically an ISA slot with an extra slot on the end. The whole thing is about 4 inches longer than an ISA slot.
• Peripheral Component Interconnect (PCI) This is the other very fast bus developed by Intel. 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, a drawback on 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 bus is most popular today with Pentiums, although occasionally you will see one on a 486.
• 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.