Intel 64 and IA-32 Architectures Software Developers Manual Volume 1, Basic Architecture

2-18 Vol. 1

INTEL

64 AND IA-32 ARCHITECTURES

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.

HT Technology leverages the process and thread-level parallelism found in contem-

porary operating systems and high-performance applications by providing two or

more logical processors on a single chip. This configuration allows two or more

threads

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.

2.2.5.1 Some Implementation Notes

All HT Technology configurations require:

• A processor that supports 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 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 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 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.

2.2.6 Multi-Core Technology

Multi-core technology is another form of hardware multi-threading capability in IA-32

processor families. Multi-core technology enhances hardware multi-threading capa-

bility by providing two or more execution cores in a physical package.

The Intel Pentium processor Extreme Edition is the first member in the IA-32

processor family to introduce multi-core technology. The processor provides hard-

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

“process” and “thread.”