AMD-K6-2E/400AFR AMD [Advanced Micro Devices], AMD-K6-2E/400AFR Datasheet - Page 29

• Manufacturer Part Number: AMD-K6-2E/400AFR
• Manufacturer: AMD [Advanced Micro Devices]

22529B/0—January 2000
Branch Logic
3DNow!™ Technology
Chapter 2
T h e A M D -K 6 -2 E p r o c e s s o r i s d e s i g n e d w i t h h i g h ly
sophisticated dynamic branch logic consisting of the following:
The AMD-K6-2E processor implements a two-level branch
prediction scheme based on an 8192-entry branch history table.
The branch history table stores prediction information that is
used for predicting conditional branches. Because the branch
history table does not store predicted target addresses, special
address ALUs calculate target addresses on-the-fly during
instruction decode.
Th e b ra n ch t a rg e t c a ch e a u g m e n t s p re d i c t e d b ra n ch
performance by avoiding a one clock cache-fetch penalty. This
specialized target cache does this by supplying the first 16 bytes
of target instructions to the decoders when branches are
predicted. The return address stack is a unique device
specifically designed for optimizing CALL and RETURN pairs.
In summary, the AMD-K6-2E processor uses dynamic branch
logic to minimize delays due to the branch instructions that are
common in x86 software.
AMD has taken a lead role in improving the multimedia and 3D
capabilities of the x86 processor family with the introduction of
3DNow! technology, which uses a packed, single-precision,
floating-point data format and Single Instruction Multiple Data
(SIMD) operations also found in the MMX technology model.
An analogous set of 21 registers is available specifically for
MMX and 3DNow! operations.
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Branch history/Prediction table
Branch target cache
Return address stack
that correspond to the x86 general-purpose registers—
Twelve of these are MMX/3DNow! rename registers.
Nine are MMX/3DNow! committed or architectural
registers, consisting of one scratch register and eight
registers that correspond to the MMX registers (mm0–
mm7). For more detailed information, see the 3DNow!™
Technology Manual, order #21928.
EAX, EBX, ECX, EDX, EBP, ESP, ESI, and EDI.
Internal Architecture
AMD-K6™-2E Processor Data Sheet
11