This section summarizes the basic design requirements for ISA. All ISA cards that receive a "Designed for Microsoft Windows" logo must meet the requirements defined in this section in addition to meeting the general expansion card requirements as defined in the "Basic PC 97" chapter in Part 2 of this guide.
1. ISA support in PC system
| Optional |
System designers are encouraged to consider designing PC systems that do not include the ISA bus or that do not allow for end-user insertion of ISA devices, and hardware vendors are encouraged to plan for complete migration away from ISA.
The requirements listed in this chapter apply only if the manufacturer chooses to include ISA support in a system.
2. System supports Plug and Play ISA specification and Plug and Play BIOS
| Required |
If ISA support is included in a PC 97 system, the manufacturer must implement the standards described in the following Plug and Play specifications:
A Plug and Play – compliant system can identify the Plug and Play ISA cards and the resources they use, then program these resources so they do not conflict. The conflict-resolution scheme used on Plug and Play ISA cards essentially puts all cards "to sleep," then reads the card identification, the information about what the card can do, and the resources it requires. This information can include what resources are programmable and the ranges they can be programmed. With this information, the system can configure the card in a way that prevents conflicts with other cards in the ISA bus.
For this procedure to work, the system must completely implement the related requirements defined in the Plug and Play ISA specification and the Plug and Play BIOS specifications.
Note Standard system devices are excluded from this requirement. The system can reserve static resources for devices such as interrupt controllers 1 and 2, timer (8254-2), keyboard controller (8042), real-time clock, DMA page registers, DMA controllers 1 and 2, and math coprocessor (if present). For an x86-based system, these fixed resources are located at I/O addresses under 100h and can also include an NMI mask.
3. BIOS configures ISA cards on non – Plug and Play operating systems
| Required |
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.
To identify whether a Plug and Play operating system is present, the BIOS first evaluates the master boot record to find the partition from which to boot and then determines whether that partition is a Windows 95 partition. The Windows 95 signature in the partition boot sector is the string "MSWIN4.0" located at offset 03h in the partition boot record.