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6-6 Technical Information
Microprocessor
The 80286 is a high-performance microprocessor with a 16-bit external
data path, up to 16 megabytes of directly addressable physical
memory and up to 64 terabytes of virtual memory space. The operating
speed of the 80286 chip is 6MHz in Normal mode and 12MHz in Turbo
mode.
The 80286 operates in two modes: protected virtual address mode and
real address mode.
Protected Virtual Address Mode
The virtual address mode provides a 1 -gigabyte virtual address space
mapped onto a 16 megabyte physical address space. Virtual address
space is larger than physical address: the use of a virtual address that
does not map to a physical address location will cause a restartable
interrupt.
This mode uses 32-bit pointers that consist of a 16-bit selector and
offset components. The selector specifies an index into a memory-
resident table and the 24-bit base address of the desired segment is
obtained from the memory table. A 16-bit offset is added to the
segment base address to form the physical address. The microproces-
sor automatically references the tables whenever a segment register
is loaded with a selector. Instructions that load a segment register will
refer to the memory based tables without additional program support.
The memory-based tables contain 8-byte values called descriptors.
Chapter 6: Appendix
17
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