IBM JAGUAR V 386, System Manual

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GENERAL FEATURES
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PROCESSOR
80386DX is a 32-bit microprocessor with 32-bit
external data bus and 32-bit external address bus.
Therefore it processes more data at the same time than
80286 and can access a large memory size which is
necessary for 32-bit applications. To combine the wider
bus structure and all the advanced functions on chip,
total 275,000 transistors are integrated together.
80386DX is aimed to provide advanced facilities
to sophisticated software, but still remains compatible
with existing software in the market. It can operate at
real mode and protected mode. In Real mode the 386DX
operates as a very fast 8086, but with 32-bit extensions
if desired. Real mode is required primarily to setup the
processor for Protected mode operation. Protected mode
provides access to the sophisticated memory
management, paging and privilege capabilities of the
processor. Furthermore, new mechanism allows
switching between Real mode and Protected mode at
high speed operation.
The Protected mode of 80386 is fully compatible
with 80286. All privilege - level and I/O protection
system are supported. New system control instructions,
memory paging, I/O permission bit map are provided to
make 80386 ideal for multi-tasking operation systems.
In addition, a virtual 8086 mode is provided. In
this mode, the CPU can be considered by the programs
as being divided into several 8086 CPUs and each
program has their own CPU and memory space. Several
programs for XT/AT as well as operating systems for
80286 and 80386DX can be executed simultaneously.
Programs are isolated and protected from each other by
80386DX. Each program can be considered as running
at a XT/AT.
80386DX includes many new instructions for
system control, high level language support and