AMD-K6 Datasheet, PDF (39/346 Pages) Advanced Micro Devices – AMD-K6 Processor

20695H/0—March 1998
Preliminary Information
AMD-K6^® Processor Data Sheet
3
Software Environment
This chapter provides a general overview of the AMD-K6
processor’s x86 software environment and briefly describes the
data types, registers, operating modes, interrupts, and
instructions supported by the AMD-K6 architecture and design
implementation.
3.1
Registers
General-Purpose
Registers
The AMD-K6 processor contains all the registers defined by the
x86 architecture, including general-purpose, segment,
floating-point, MMX, EFLAGS, control, task, debug, test, and
descriptor/memory-management registers. In addition, this
chapter provides information on the AMD-K6 Model-Specific
Registers (MSRs).
Note: Areas of the register designated as Reserved should not be
modified by software.
The eight 32-bit x86 general-purpose registers are used to hold
integer data or memory pointers used by instructions. Table 2
contains a list of the general-purpose registers and the
functions for which they are used.
Table 2. General-Purpose Registers
Register
Function
EAX Commonly used as an accumulator
EBX Commonly used as a pointer
ECX Commonly used for counting in loop operations
EDX Commonly used to hold I/O information and to pass parameters
EDI Commonly used as a destination pointer by the ES segment
ESI Commonly used as a source pointer by the DS segment
ESP Used to point to the stack segment
EBP Used to point to data within the stack segment
In order to support byte and word operations, EAX, EBX, ECX,
and EDX can also be used as 8-bit and 16-bit registers. The
shorter registers are overlaid on the longer ones. For example,
the name of the 16-bit version of EAX is AX (low 16 bits of
EAX) and the 8-bit names for AX are AH (high order bits) and
Chapter 3
Software Environment
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