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HIGHTLIGTHS
protection system and can therefore be used by
all applications, including those that
will
run in
production without protection. More impor-
tantly, they provide the ability to set data
breakpoints in addition to the more familiar
instruction breakpoints. The 80386 monitors all
four current break point addresses simultaneously
without slowing execution.
Instruction breakpoints trap (typically to a de-
bugger) when
an
instruction
is
executed; most
processors provide this capability with a special
instruction that the debugger writes over the
instruction
of
interest.
By
specifying instruction
breakpoint addresses in registers, the 80386
eliminates the contortions required to write
breakpoint instructions into protected
or
shared
code. Data breakpoints, which are
an
exceptional
capability for a microprocessor, are a particularly
useful debugging tool. A data breakpoint can
trap the instant that
an
address
is
read,
or
is
either read
or
written. Using data breakpoints, a
programmer can, for example, immediately locate
the instruction responsible for erroneously over-
writing a data structure.
In
addition to the breakpoint registers, the 80386
provides the more conventional debugging fa-
cilities
of
a breakpoint instruction and single
stepping.
1.6 Object Code Compatibility
Two
generations
of
86 family processors have
preceded the 80386, the 80286 and the 8086, and
the 80386
is
compatible
at
the binary
level
with
both
of
them. This compatibility preserves soft-
ware investments, allows rapid market entry, and
can provide access to the vast library
of
software
written for computers based on the 86
family.
Of
course the 80386 can run 8086 programs;
it
can also run 80286 and 80386 programs concur-
rently. But the 80386's most innovative compati-
bility feature
is
Virtual 86 capability, which
establishes a protected 8086 environment within
the 80386 multitasking framework. Comple-
1-4
menting the Virtual 86 facility, 80386 paging can
be used
to
give each Virtual
86
task a one-
megabyte address space anywhere in the
80386
physical address space. Moreover, if the 80386
operating system supports virtual memory, Vir-
tual 86 tasks can be swapped like other tasks
without special attention.
In
short, the 80386's
Virtual 86 facility permits three generations of86
family software to run at the same time.
1.7 Summary
The
80386
provides the raw performance required
to implement high-end microprocessor-based
systems. The 80386 architecture
is
flexible: rather
than being bound to one view of the machine,
system designers can choose the options that best
match the needs of the application. Complete
memory management facilities, including support
for segmentation, paging, and virtual memory,
are available on-chip.
Up to four levels of
protection can be used to build
"firewalls"
between software components,
or
protection can
be
forgone altogether. Virtual 86 tasks can enrich
32-bit systems with the extraordinary array
of
standard software already developed for business
and other
86
family machines.
The power and versatility
of
the 80386 can be
augmented by other Intel chips that can help
maximize system performance. These include
local area network controllers, advanced
DMA
controllers, disk controllers,
and
graphics
coprocessors.
Design time and cost can be reduced with the aid.
of
I ntel development tools and boards. Develop-
ment tools include compilers, linking and loading
utilities, operating systems, and
an
in-circuit
emulator
(ICP
M
386). Hundreds of industry
standard
MULTIBUS® I boards are available
to perform standard functions without incurring
design and test costs;
-the array
of
high-
performance
MULTIBUS
II
boards
is
growing
rapidly. Finally, Intel's experienced staff
of
appli-
cation engineers and specialists can provide
design assistance worldwide.