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

Vol. 1 2-17
INTEL
®
64 AND IA-32 ARCHITECTURES
2.2.5 Hyper-Threading Technology
Hyper-Threading (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 tech-
nology enables a single physical processor to execute two or more separate code
streams (threads) concurrently using shared execution resources.
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.
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 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 registers, 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 HT Technology (imple-
mented with two logical processors) and a traditional dual processor system.
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 HT Tech-
nology share the core resources of the physical processor. This includes the execution
Figure 2-5. Comparison of an IA-32 Processor Supporting Hyper-Threading
Technology and a Traditional Dual Processor System
Processor Core Processor CoreProcessor Core
AS ASASAS
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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