System Buses for Basic PC 97

This section defines the general requirements for system buses. Additional requirements are defined in Part 3 of this guide for particular buses.

25. Universal Serial Bus with one USB port, minimum

Recommended: 2 ports. Universal Serial Bus (USB) provides a bidirectional, isochronous, dynamically attachable serial interface for adding peripheral devices such as game controllers, communications devices, and input devices on a single bus.

The USB implementation in the system must meet the requirements defined in USB specifications, plus any additional requirements for PC 97 defined in the "USB" chapter in Part 3 of this guide.

26. Support for other high-speed expansion capabilities

Additional support for expansion capabilities can be provided using PCI v. 2.1, IEEE 1394, CardBus, or other high-speed buses. For a mobile PC, one CardBus slot is required, and two slots are recommended. Any expansion bus implemented in the system must meet the requirements defined in the related chapter in Part 3 of this guide.

27. If present, PCI bus meets PCI v. 2.1 and higher, plus PC 97 requirements

If PCI is used in a PC system, the PCI bus must meet the requirements defined in PCI v. 2.1 or higher, plus any additional requirements for PC 97 defined in the "PCI" chapter in Part 3 of this guide. Exceptions for particular devices are noted in Part 3 and Part 4.

For example, add-on PCI IDE devices must comply with PCI 2.1 requirements and also provide Subsystem IDs and Subsystem Vendor IDs, but PCI-to-PCI bridges and core chip sets do not have to provide Subsystem IDs and Vendor Subsystem IDs.

28. ISA expansion bus

It is recommended that system designers consider not providing expansion capabilities using the ISA bus in PC 97 systems and that all hardware vendors plan for migration away from ISA in their product lines. However, the PC system designer might choose to include the ISA expansion bus to support customers who want to "recycle" legacy add-on hardware.

If ISA is implemented in a PC 97 system, the following is required:

• Complete Plug and Play support must be implemented as defined in Plug and Play ISA Specification v. 1.0a. For x86-based systems, this includes support in the system BIOS and support for ISA option ROMs. These requirements include a means for identifying the Plug and Play capabilities of the option ROM and enabling the option ROM to determine whether the system BIOS is compatible with Plug and Play.
• Resource configuration requirements are specified for each physical port or device on the system and cannot be split among devices of the same type. This ensures true Plug and Play resource assignment and conflict resolution in the system. These minimum resource requirements are defined in the chapters for specific device classes in Part 4 of this guide.

  If the device cannot meet the resource requirements defined for PC 97, ISA IRQ sharing must be supported in the hardware and driver for an ISA device by using the operating system support first provided in 1996 for Windows 95.

• As specified in the Plug and Play ISA specification, a card must have both an industry-unique Vendor ID and a company-unique Product Identifier. This means that each different product and model from the same manufacturer must have a different product identifier to ensure that the operating system can isolate and identify these different cards.

  The use of a unique serial number is strongly recommended. To avoid problems that can occur when a user installs two of the same cards in a PC system, the Plug and Play ISA specification defines a unique serial number field that can be added to the Vendor and Product IDs to make the card completely unique. If unique serial numbers are not supported, the Serial Number field must contain 0xFFFFFFFF, as required in the Plug and Play ISA specification.

• The system BIOS must properly configure all Plug and Play ISA cards in the PC system if a non – Plug and Play operating system is loaded.

Notice that including ISA in the system will probably require support for traditional keyboard, parallel, and serial ports. For related requirements, see the "Serial, Parallel, and Wireless Support" and "Input Components" chapters in Part 4 of this guide. For a complete list of ISA requirements for PC 97, see the "ISA" chapter in Part 3 of this guide.