80286
Processor
HP
Vectra
PC
utilizes the Intel 80286 microprocessor. The 80286
has
a 24-bit address bus
(a
16 Mbyte physical address range), a
16-bit data
bus,
and a comprehensive instruction set. The 80286
supports
two
addressing modes: the real-address mode and the
protected mode.
These
modes
of
operation are detailed
in
the
following sections.
Real-Address
Mode
In
real-address mode the 80286 operates
as
a high performance
8086. It supports 1 Mbyte
of
contiguous system memory using 20
address bits
(AO-A
19). With a
few
differences (which are
described
in
the
HP
Vectra Technical Reference
Manual
Volume
2:
System
BIOS
the 80286
is
object code compatible
with
the
8088
and 8086 microprocessors.
In
addition,
the
80286 supports
several
new
instructions
in
the real-address mode
not
found
in
the
8088 or 8086. All system software (i.e.,
ROM
BIOS,
MS-DOS
Version 3.1, etc.) currently operates only
in
the real-address mode.
Protected Operating
Mode
The protected mode allows the
use
of
the extended features
of
the 80286.
These
include 1 Gigabyte
of
virtual address space, 16
Mbytes
of
physical address
space,
on-board memory
management, and four-level memory protection. The protected
mode
is
designed
to
support multitasking/multiuser operating
systems and highly advanced languages. When the 80286
is
operating
in
the protected mode, it
is
not
object code compatible
with
the 8088 and 8086 software.
Several
new
instructions are
provided
in
the protected mode
to
control these advanced
features.
These
instructions are
not
compatible
with
the 8088,
8086, or the 80286 operating
in
the real-address mode.
Processor Board 13
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