Specifications
2.5.1 Normal Use of SCSI
The board's SCSI bus interface can serve a variety
of
purposes, including connection of hard
disk controllers, tape controllers, text scanners,
and
printer
and
communications servers.
Support is provided by the
board's ROM-BIOS for booting of DOS from a SCSI
de'Ace
such
as a
hard
disk. Virtually any device compatible with the SCSI
Common
Command
Set for
direct
access
devices
can
be
used through the ROM-BIOS support. Some examples
of
direct
access
SCSI devices that can
be
accessed as DOS drives are hard disk drives, magnetic bubble
drives, high density floppy drives, and some tape drives.
The
Little
Board/PC
comes with a diskette containing software utilities for normal
DOS
operation using hard disks and other SCSI direct access devices. A powerful SCSI formatting
utility is included that allows low-level formatting, changing the interleave, and mapping out
bad sectors. Refer to Chapter 4 for information
on
software
~tup
and drive preparation.
PC-DOS version
3.x
requires that drives larger than 32 megabytes be partitioned into more
than one "partition", while
DR-DOS, MS-DOS
4.x,
and
PC-DOS
4.x
allow such drives to
be
used without partitioning. Under PC-DOS or MS-DOS
3.x,
each drive can
be
logically parti-
tioned into as many as four partitions, 32 megabytes
or
smaller, allowing the use
of
physical
drives as large as 128 megabytes.
DR-DOS,
MS-DOS 4.x,
and
PC-DOS
4.x support a
maximum drive size
of
512M bytes.
There are several other types
of
SCSI devices besides direct access devices. SCSfs additional
device types include
sequentk1l
access
devices
(e.g. tape),
printer
devices,
read-only
devices
(e.g.
CD-ROM), and
processor
devices
(e.g. CPU's).
In
general, these other device types require
special application programs, utilities,
or
driver software for use.
Hard
disk
support
for
operating
systems
other
than
DOS
mayor
may
not
be
automatically
available through the board's
ROM-BIOS resident hard disk driver. This depends
on
wheth-
er
the operating system in question uses BIOS calls exclusively for the
hard
disk function, and
whether the operating
system has any special ROM-BIOS constraints (such as re-entrancy).
Some operating systems -- multitasking ones in particular such as Unix -- interface directly
with
the
hardware
(e.g.
attempt
to
directly program a bus
hard
disk
controller)
and bypass
BIOS.
In
those situations, the operating system must be modified
to
add
an
appropriate SCSI
hard disk driver to use the
to
take advantage
of
the board's SCSI interface.
2.5.2 The Ampro SCSI/BIOS
Through the universal bus interface
and
command protocols offered by SCSI, it is possible to
connect a wide variety
of
mass storage devices to a computer system with virtually no changes
to
system
software.
To
this,
Ampro
has
added
a
further
layer
of
universality:
the
SCSI/BIOS.
As its name implies, the SCSI/BIOS consists
of
a set of low level functions which have
been
incorporated
into the
ROM-BIOS
to
provide a hardware
independent
interface between
system software
and
peripheral
devices connected
to
the
SCSI bus.
The
advantage
of
the
Ampro
SCSI/BIOS
is
that
programmers
can
write software
that
uses devices connected to
the
SCSI bus without having
to
be
concerned with the details
of
operating the board's SCSI
bus interface. Also, software
can
be
ported
to
the Little
Board/PC
from
other
hardware
environments much faster due
to
the presence of the SCSIIBIOS, and with less difficulty and
risk.
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