This section summarizes class specifications and standards for SCSI host adapters.
1. Host controller supports bus mastering
Required
The host controller must support bus mastering.
2. Bootable SCSI controller supports El Torito No Emulation mode
Required
A bootable SCSI storage controller must support the No Emulation mode defined in El Torito—Bootable CD-ROM Format Specification, Version 1.0, by IBM and Phoenix, or an equivalent method that supports the Windows NT CD-ROM installation process.
3. Option ROMs support Int 13h Extensions
Required
The Int 13h Extensions ensure correct support for high-capacity drives, consistent drive-letter mapping between real and protected modes, and other capabilities for both Windows and Windows NT. Support for the fixed-disk access subset of Int 13h Extensions must be provided in the system BIOS and in any option ROMs for storage devices that include BIOS support. The Int 13h Extensions are defined in the Windows NT 5.0 DDK and in the “Layered Block Device Drivers” section of the Windows 98 DDK.
4. Option ROMs support virtual DMA services
Required
Plug and Play SCSI host adapters must support virtual DMA services in the host-adapter option ROM and must support bus mastering. Virtual DMA supports scatter/gather capabilities, solving the problem of mapping linear addresses (segment:offset) into physical addresses.
5. Bus type is clearly indicated on connectors for all adapters, peripherals, cables, and terminators
Required
Connectors for each SCSI adapter, peripheral, cable, and terminator must be clearly labeled to indicate the bus type. All external SCSI connectors must display the appropriate SCSI icon defined in Small Computer Interface (SCSI-3) Parallel Interface (SPI) specification, Annex F, and must display any clarifying abbreviations or acronyms.
6. Differential devices support DIFFSENS as defined in SCSI-3 specification
Required
Without DIFFSENS, the differential bus drivers and/or a single-ended device will burn up if a single-ended device is put on a differential bus.
The specification for DIFFSENS is defined in Section 5.4.2 of the SCSI-3 specification.
7. Automatic termination circuit meets SCSI-3 specification
Required
SCSI add-on adapters and on-board controllers must use automatic termination, which allows a user to add external devices without removing the PC case. Terminators used in the SCSI host adapter must be regulated terminators, also known as active, SCSI-3 SPI, SCSI-2 alternative-2, or Boulay terminators.
8. SCSI terminator built onto internal cables meets SCSI-3 specification
Required
For SCSI subsystem configurations, internal cables must be preconfigured with active termination at one end of the cable.
9. Terminator power is supplied to the SCSI bus with over-current protection
Required
For system-board implementations using PCI or another expansion bus, the host adapter must supply terminator power (TERMPWR) to the SCSI bus. All terminators on the host adapter, as well as those on the internal and external SCSI bus, must be powered from the TERMPWR lines on the SCSI bus.
Devices that provide TERMPWR must also provide some means of limiting the current, through use of a self-setting device. For example, a positive-temperature coefficient device or circuit breaker can be designed into the circuit. These devices open during an over-current condition and close after the condition ends.
This item is a recommendation for battery-powered systems that implement the SCSI host adapter as a PC Card device, because of battery power-consumption issues.
10. External connector meets SCSI-2 or higher specification
Required
If an external connector is implemented, it must be a high-density connector and must meet the requirements defined in the SCSI-2 or higher specification.
11. Internal terminator is as close as possible to the last peripheral on the cable
Recommended
The internal terminator should be as physically close as possible to the last peripheral on the cable. There should be some means, such as written instructions on the cable, to ensure that the user always connects internal peripherals starting with the plug closest to the terminator.