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An NCR SCSI controller or processor can control peripherals such
as hard disk drives, CD-ROM drives, tape drives, and removable
media. SCSI peripherals are "intelligent" devices that do not need
the constant attention required by "non-intelligent" devices. Up to
15 SCSI peripheral devices can be connected (via the SCSI bus) to
a SCSI host bus adapter card on which the SCSI controller or
processor resides. A SCSI host bus adapter can also function as a
secondary adapter in a system which already has a primary hard
drive controller card (lDE, ESDI, ST506). Only SCSI host bus
adapters will do this, expanding the possibilities for system
configuration.
A SCSI BIOS is the bootable ROM code that manages SCSI
hardware resources. It is specific to a family of NCR SCSI
controllers or processors. An NCR SCSI BIOS integrates with a
standard system BIOS, extending the standard disk service routine
provided through INT13. It is also responsible for processing and
executing SCSI requests communicated from a SCSI device driver
or application. An important feature of the SCSI BIOS is that it is
completely operating system independent. All ROM based SCSI
BIOS support booting from a SCSI hard disk and can be ported to
a variety of hardware platforms. They also support 16- and 32-bit
operating systems running under real or protected addressing
modes.
The NCR SCSI BIOS provides a hardware independent interface
which isolates the operating system drivers and SCSI application
programs from the underlying hardware. This enables a single
driver to work with any host adapter or SCSI controller which has
an NCR SCSI BIOS. During its boot time initialization, the SCSI
8I05 determines if another hard disk is already installed. If there is,
the SCSI BIOS will map any SCSI drives it finds behind the drive
already installed. Otherwise, the SCSI BIOS will install drives
starting with the system boot drive. In this case, the system will
boot from a drive controlled by the SCSI BIOS. If the operating
system used is DOS 5.0 or above, the SCSI BIOS allows access to
Chapter 5 SCSI Drive Installation
43
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