Vol. 1 2-17

INTEL

®

 64 AND IA-32 ARCHITECTURES

2.2.8 Intel

®

 Hyper-Threading Technology

Intel Hyper-Threading Technology (Intel HT Technology) was developed to improve the performance of IA-32 
processors when executing multi-threaded operating system and application code or single-threaded applications 
under multi-tasking environments. The technology enables a single physical processor to execute two or more 
separate code streams (threads) concurrently using shared execution resources. 
Intel HT Technology is one form of hardware multi-threading capability in IA-32 processor families. It differs from 
multi-processor capability using separate physically distinct packages with each physical processor package mated 
with a physical socket. Intel HT Technology provides hardware multi-threading capability with a single physical 
package by using shared execution resources in a processor core.
Architecturally, an IA-32 processor that supports Intel HT Technology consists of two or more logical processors, 
each of which has its own IA-32 architectural state. Each logical processor consists of a full set of IA-32 data regis-
ters, segment registers, control registers, debug registers, and most of the MSRs. Each also has its own advanced 
programmable interrupt controller (APIC). 
Figure 2-5 shows a comparison of a processor that supports Intel HT Technology (implemented with two logical 
processors) and a traditional dual processor system. 

Figure 2-4.  SIMD Extensions, Register Layouts, and Data Types

4 Packed Word Integers

8 Packed Byte Integers

2 Packed Doubleword Integers

MMX Registers

Quadword

MMX Technology - SSSE3

Data Type

Register Layout

SIMD Extension

SSE - AVX

4 Packed Single-Precision

Floating-Point Values
2 Packed Double-Precision

Floating-Point Values

8 Packed Word Integers

16 Packed Byte Integers

4 Packed Doubleword

2 Quadword Integers

Double Quadword

Integers

XMM Registers

8 Packed SP FP Values

4 Packed DP FP Values

YMM Registers

AVX

2 128-bit Data