2-18 Vol. 1

INTEL

®

 64 AND IA-32 ARCHITECTURES

Unlike a traditional MP system configuration that uses two or more separate physical IA-32 processors, the logical 
processors in an IA-32 processor supporting Intel HT Technology share the core resources of the physical 
processor. This includes the execution engine and the system bus interface. After power up and initialization, each 
logical processor can be independently directed to execute a specified thread, interrupted, or halted.
Intel HT Technology leverages the process and thread-level parallelism found in contemporary operating systems 
and high-performance applications by providing two or more logical processors on a single chip. This configuration 
allows two or more threads

1

 to be executed simultaneously on each a physical processor. Each logical processor 

executes instructions from an application thread using the resources in the processor core. The core executes these 
threads concurrently, using out-of-order instruction scheduling to maximize the use of execution units during each 
clock cycle.

2.2.8.1  

Some Implementation Notes

All Intel HT Technology configurations require:

•

A processor that supports Intel HT Technology

•

A chipset and BIOS that utilize the technology

•

Operating system optimizations

See 

http://www.intel.com/products/ht/hyperthreading_more.htm

 for information.

At the firmware (BIOS) level, the basic procedures to initialize the logical processors in a processor supporting Intel 
HT Technology are the same as those for a traditional DP or MP platform. The mechanisms that are described in the 
Multiprocessor Specification, Version 1.4 to power-up and initialize physical processors in an MP system also apply 
to logical processors in a processor that supports Intel HT Technology. 
An operating system designed to run on a traditional DP or MP platform may use CPUID to determine the presence 
of hardware multi-threading support feature and the number of logical processors they provide.
Although existing operating system and application code should run correctly on a processor that supports Intel HT 
Technology, some code modifications are recommended to get the optimum benefit. These modifications are 
discussed in Chapter 7, “Multiple-Processor Management,” Intel® 64 and IA-32 Architectures Software Developer’s 
Manual, Volume 3A.

Figure 2-5.  Comparison of an IA-32 Processor Supporting Hyper-Threading Technology and a Traditional Dual 

Processor System

1. In the remainder of this document, the term “thread” will be used as a general term for the terms “process” and “thread.”

Processor Core

Processor Core

Processor Core

AS

AS

AS

AS

Traditional Multiple Processor (MP) System

IA-32 Processor Supporting

Hyper-Threading Technology

AS = IA-32 Architectural State

IA-32 processor

IA-32 processor

Two logical 
processors that share 
a single core

Each processor is a 
separate physical 
package

IA-32 processor

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