PC Hardware

Tutorial Summary: Expansion Buses

The following points summarize the key concepts in this tutorial:

Connecting Devices to the Motherboard

  • Expansion slots are standardized connections that provide a common access point for installing devices.

  • The different types of expansion bus architecture are the ISA, MCA, EISA, VESA VLB, and PCI.

  • USB architecture supports both isochronous (time-dependent) and asynchronous (intermittent) data transfers.

  • PCI architecture makes use of autoconfiguration to let the PC's BIOS assign the IRQ linking the card to the system bus.

  • AGP architecture removes display data traffic from the PCI bus.

Configuring Expansion Cards

  • In order for a CPU to keep track of its devices and communicate with them, a unique I/O address must be assigned to each device.

  • In order to prevent devices from "talking" to the CPU at the same time, an IRQ number is assigned to the devices that informs the CPU which device is requesting its attention. It is recommended that you memorize as many of the typical IRQ assignments as possible.

  • The DMA chip moves data, handling all the data passing from peripherals to RAM and vice versa.

  • To avoid problems similar to IRQ conflicts, no two devices should have the same DMA channel assignment.

  • COM ports are used for serial devices (such as modems) and LPT ports are used for parallel devices (such as printers). COM ports put these devices in direct communication with the CPU and make installation easier.

Review: Questions

  1. Why does a computer need an expansion bus?

  2. Name the available expansion buses.

  3. What happens if two non-PCI devices use the same I/O address?

  4. How many IRQs are available on most PCs?

  5. Under what conditions would a second modem-installed and assigned to COM3-not work?

  6. Identify the two divisions of the external data bus and describe the purpose of each.

  7. What is the standard that governs computer buses?

  8. What is the difference between ISA and EISA cards?

  9. Why was VESA created?

  10. What is bus mastering?

  11. Describe ways in which the PCI bus is better than previous technologies.

  12. How does the CPU use I/O addresses?

  13. What is the I/O port address of COM2?

  14. What are the functions of IRQs?

  15. List as many of the standard IRQ assignments as you can.

  16. What is the function of the DMA chip?

  17. Why is it important not to assign an IRQ to more than one device?

  18. What is the difference between COM ports and LPT ports?

  19. Why is it important to document IRQs, DMAs, and I/O addresses?