Karbosguide.com - Module 5a2.

About adapters


The contents:

  • Adapters
  • The modular PC design

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  • Typically, adapters provide functions, which are separated from the system board.
  • Adapters provide expansion capability to the PC.

    There are PCs without expansion slots. In that case all functions must be built into the system board. You could easily include chips for graphics, ethernet, SCSI, and sound on the system board. This is not common in stationary PCs. Portable, laptop PCs have nearly all electronics on the system board. This is called closed architecture.

    A traditional PC has a system board which contains all standard functions (except the graphics chip). To this system board you can add various expansion cards, which control one or more peripheral units:

  • Adapters

    In a stationary PC, adapters are typically printed circuit boards called expansion boards or expansion cards. They form a link between the central PC unit and various peripherals. This is the so-called open architecture.
    The system board Expansion boards
    Standard functions
    incl. control of keyboard,
    COM and LPT ports. and
    four EIDE units.
    Video card
    Network controller
    Sound card
    SCSI card
    3D graphics controller (for 3D games)

    Other expansion board types:

  • Internal modem (in lieu of external modem)
  • ISDN adapters
  • Extra parallel ports
  • Video editing boards
  • Special graphics cards, which supplement the usual (3D and MPEG)
  • TV and radio receivers.


    In the Pentium based PC, the hard disk is connected to an EIDE controller, which is integrated on the system board. Likewise, the serial and parallel ports are connected directly to the system board. This is new. On the 386 PCs, you had to install special controller cards (I/O cards) to handle these functions. They are included in the modern chip sets on the system board. Other functions are not integrated. That includes:


    The integrated hard disk controller

    The video controller

    You have to install a video card to make the PC function. It would be illogical to assemble a PC without a video card. You would not be able to see what you are doing, since the video card governs data transmission to the monitor.

    The advantage of this design is, that the user can choose between numerous video cards in various qualities. A discount store may offer a complete Pentium based PC (without printer) and with the cheapest video card for $669.-. If the buyer is quality oriented, he would want to spend an additional $40 to get a much better video card.



    The modular PC design

    In this way, various expansion boards provide flexibility in assembling a customized PC. At the same time, various electronics manufacturers are specializing their production:

    ASUS and Tyan are good at making system boards. Others, like S3, Matrox, and ATI specialize in making graphics chips and expansion boards. Olicom make only net boards. Adaptec make only SCSI controllers and Creative Labs make SoundBlaster sound boards.

    This variety of manufacturers offers the consumer wide choices. Your PC can be customized and configured according to your needs and wallet size.


    About the electronics

    The adapter is a printed circuit board. They have an edge connector, so they can be inserted in expansion slots in the system board. The expansion slots connect to the I/O buses. Since the Pentium system board has two I/O buses, it has two types of expansion slots:

  • ISA slots
  • PCI slots

    Typically, on a regular Pentium system board there are three or four of each type. That gives a total of 7 expansion slots. One expansion board can be installed in each of these. You simply press the edge connector of the expansion board into the expansion slot. Now it is connected to the bus.

    Here you see two PCI slots open for video cards, network controllers and others:

    Below, you see a network adapter. It is an ethernet card with PCI interface, so it fits in a PCI slot in the Pentium. This inexpensive board allows your computer to join a network with other net board equipped PCs. Please compare the edge connector at the button of the card with the sockets above. They fit together!


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    Learn more

    Read: Module 5b about EIDE, Ultra DMA and AGP.

    Read Module 5c about USB.

    Read Module 6b with a little about Windows 95/98.

    Read Module 6c about the relationship between BIOS, OS and hardware

    Read Module 7a about the videosystem

    Read about video cards in Module 7b.

    Read about digital sound in Module 7c.

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