Updated June 2004

The following overview and integration instructions are for professional system integrators building PCs that use Pentium® 4 processors supporting Hyper-Threading Technology with industry-accepted motherboards and peripherals. It contains technical information specific to Pentium 4 processors supporting Hyper-Threading Technology and is intended to aid in system integration.

Note: Before building a Pentium 4 processor-based system, consult the motherboard manual, boxed processor manual, and the Integration Overview for Systems Based on the Pentium 4 Processor in the 478-pin Package or the Integration Overview for Systems Based on the Pentium 4 processor in the 775-land package (the following information is intended to be supplementary to these documents).

• Platform Component Requirements
  • Processor Selection
  • Motherboard Selection
  • Operating System Support
• Hyper-Threading Technology Setup and Integration
• Verifying Hyper-Threading Technology in Windows* XP
• Software Considerations
• Additional Information

Hyper-Threading Technology enables a single physical processor to execute two separate code streams (called threads) concurrently, increasing processor utilization and providing greater throughput and improved performance. Architecturally, the Pentium 4 processor supporting Hyper-Threading Technology consists of two logical processors (see Figure 1), each of which has its own architectural state. The architectural state that is duplicated for each logical processor consists of the data registers, segment registers, control registers, debug registers, and most of the MSRs or Model Specific Registers. Each logical processor also has its own advanced programmable interrupt controller or APIC. After power-up and initialization, each logical processor can be individually halted, interrupted, or directed to execute a specified thread, independently from the other logical processor on the Pentium 4 processor core.

Figure 1. Comparison of a Pentium® 4 Processor Supporting Hyper-Threading Technology and a Traditional Dual Processor System

Unlike a traditional dual processor (DP) configuration that uses two separate physical processors (see Figure 1), the logical processors in a Pentium 4 processor supporting Hyper-Threading Technology share the execution resources of the processor core (see Figure 2), which include the execution engine, caches, system bus interface, and the firmware. Hyper-Threading Technology is designed to improve the performance of Pentium 4 processors by maximizing the use of available execution resources in the Intel® NetBurst™ microarchitecture, and exploiting the multi-threaded nature of contemporary operating systems (see Operating System Support).

Figure 2. Intel® NetBurst™ Microarchitecture Duplicated and Shared Resources for Pentium® 4 Processors Supporting Hyper-Threading Technology
Most contemporary operating systems (including Microsoft* Windows* XP and Linux*; See Operating System Support for details) divide their workload into processes and threads that can be independently scheduled and dispatched to run on two or more processors. The same division of workload can be found in many multi-threaded applications. Hyper-Threading Technology leverages the process- and thread-level parallelism found in contemporary operating systems and multi-threaded applications by allowing threads to be executed on separate logical processors. Instructions from both threads are simultaneously dispatched for execution by a single Pentium 4 processor using out-of-order instruction scheduling to keep as many of its execution units as possible busy during each clock cycle. Multi-tasking environments can also benefit from Hyper-Threading Technology. Concurrent applications can resemble multi-threaded application workloads to the processor, as each program issues an independent thread for execution. Hyper-Threading Technology provides increased processing efficiency which is passed on to the PC user in the form of better responsiveness and immediate performance when running concurrent applications.

To understand how Hyper-Threading Technology improves resource utilization, Figure 3 shows an example comparing a traditional single processor (SP) system (Figure 3A), traditional dual processor (DP) system (Figure 3B), and a system based on a Pentium 4 processor supporting Hyper-Threading Technology (Figure 3C). The SP system contains one superscalar processor that can execute up to three instructions every cycle and allows a single thread ("Thread 1", shown in orange) to be executed on this single (or physical) processor. The DP system contains two superscalar processors that can each execute up to three instructions every cycle and allows two separate threads to be executed on each (physical) processor ("Thread 1" and "Thread 2", shown in orange and blue respectively). As shown in Figure 3A and 3B, each box within each processor represents an execution unit. Each set of three horizontal boxes within each processor shows how the three execution units are being used during a given clock cycle. If a box is white, that execution unit is idle during the given clock cycle (for example, if one box is white during a clock cycle, then 1/3 of the resources are idle and 2/3 of the resources are utilized during that clock cycle). The vertical sets indicate the utilization of the three execution units over time (during multiple clock cycles). The more white boxes, the less efficient the utilization of execution resources. Sometimes all the execution resources within a processor are being used, and sometimes there are idle resources that are waiting due to cache misses, branch mispredictions, or instruction dependencies for each thread.

Figure 3C shows the result of system based on the Pentium 4 processor supporting Hyper-Threading Technology. This configuration allows the Pentium 4 processor supporting Hyper-Threading Technology to execute two separate threads simultaneously ("Thread 1" and "Thread 2", shown in orange and blue respectively), one thread for each logical processor. The Pentium 4 processor supporting Hyper-Threading Technology is utilizing the execution units more frequently and reducing idle time on the processor. Resource utilization can increase significantly for the Pentium 4 processor supporting Hyper-Threading Technology, but it is dependent on how each application is designed to use threading and the resources with the processor. For example, if an application is multi-threaded in such a way that different threads can use different resources in parallel (such as scheduling integer computation-intensive work on one logical processor while running floating-point computations on the other), then throughput for the processor can increase significantly. Pentium 4 processors supporting Hyper-Threading Technology increase instruction processing throughput and can take advantage of otherwise idle processor resources, which improve performance on both multi-threaded applications and multi-tasking environments.


Figure 3. Comparison of Execution on a Traditional Single Processor System, a Traditional Dual Processor System, and a Pentium® 4 Processor-based System Supporting Hyper-Threading Technology
(Note: This figure is a demonstration of the concepts underlying Hyper-Threading Technology and does not attempt to show the resource utilization patterns of any existing processors or software application).

Platform Component Requirements
Enabling Hyper-Threading Technology on a Pentium 4 processor-based system requires all of the following platform components:

• Intel® Pentium® 4 processor supporting Hyper-Threading Technology
• A motherboard that supports Hyper-Threading Technology
• An operating system that includes optimizations for Hyper-Threading Technology

Processor Selection
Pentium 4 processors supporting Hyper-Threading Technology also support the 533 MHz and 800 MHz system bus (Not all 533MHz system bus processors support Hyper-Threading Technology).

Motherboard Selection
Motherboards used with the Pentium 4 processor supporting Hyper-Threading Technology must utilize a chipset which supports the Intel NetBurst microarchitecture and Hyper-Threading Technology. Table 1 shows a listing of Intel® Chipsets which support the Intel NetBurst microarchitecture and Hyper-Threading Technology.

Note: Ensure that you are using a motherboard that supports the specified system bus speed for your processor system bus. Failure to use an appropriate motherboard may result in running your processor out of specification, which will void your processor warranty. Consult your motherboard manufacturer for compatibility.

Table 1. Intel® Chipsets Supporting Hyper-Threading Technology

It is important to verify that the specific motherboard model and revision support the specific Pentium 4 processor speed being used. A BIOS upgrade may be required in order to properly recognize and initialize the latest stepping of the Pentium 4 processor. The BIOS must also incorporate procedures or enhancements to enable multi-threading capability, for Pentium 4 processors supporting Hyper-Threading Technology. A BIOS upgrade may also be required in order to ensure support for Hyper-Threading Technology. See Hyper-Threading Technology Setup and Integration, for information on how to enable Hyper-Threading Technology for the system in BIOS settings.

Operating System Support
Microsoft* Windows* Operating System Based PCs

The following desktop operating systems include optimizations for HT Technology and are currently eligible to carry the new Intel® Pentium® 4 Processor with HT Technology logo:

• Microsoft* Windows* XP Professional Edition
• Microsoft* Windows* XP Home Edition

• Microsoft Windows 2000 (all versions)
• Microsoft Windows NT* 4.0
• Microsoft Windows Me
• Microsoft Windows 98
• Microsoft Windows 98 SE

• Red Hat Linux* 9 (Professional and Personal versions)
• SuSE Linux* 8.2 (Professional and Personal versions)
• Red Flag Linux* Desktop 4.0
• COSIX* Linux* 4.0

1. Enable Hyper-Threading Technology in BIOS Settings
2. Install Operating System
3. Install Latest Service Pack or Patch
4. Install Intel INF Installation Utility
5. Install latest Drivers

Enable Hyper-Threading Technology in BIOS Settings
Ensure you check the BIOS default setting prior to installation of the operating system. For your specific motherboard, ensure the switch to enable or disable Hyper-Threading Technology in BIOS settings is configured properly for Hyper-Threading Technology support. If the BIOS does not support Hyper-Threading Technology and a Pentium 4 Processor supporting Hyper-Threading Technology is installed in the motherboard, the switch to enable or disable Hyper-Threading Technology may not be present. Ensure that the latest BIOS is installed and supports Hyper-Threading Technology. Then, enter BIOS settings and configure the switch to turn-on the Hyper-Threading Technology feature.

For Intel® Desktop Boards which support Hyper-Threading Technology, Hyper-Threading Technology will be enabled in the BIOS settings by default. To check that Hyper-Threading Technology is enabled for Intel Desktop Boards, enter BIOS settings and select "Enabled" under the Hyper-Threading Technology selection (See Figure 4). If the BIOS supports Hyper-Threading Technology and a Pentium 4 Processor 2.80 GHz (or below) without Hyper-Threading Technology is installed in an Intel Desktop Board, the Hyper-Threading Technology switch will be "grayed-out" and is disabled by default.

Figure 4. Enabling Hyper-Threading Technology in BIOS Settings for Intel® Desktop Boards

Install Operating System
Install the operating system. See Operating System Support for more information.

Install Latest Service Pack or Patch
Intel recommends using Service Pack 1 (SP1) with Windows* XP Home or XP Professional. It is always good practice to use the most current version of the operating system. In addition, Microsoft has incorporated several features in SP1 for Windows XP to address common application issues and improve compatibility with MP environments, including Hyper-Threading Technology. Windows XP Service Pack 1 is available at http://www.microsoft.com/downloads/Search.aspx?displaylang=en. <sup>†

†</sup>The following links will take you off of the Intel Web site. Intel does not control the content of this linked Web site.

Install Intel INF Installation Utility
As with all of the new Intel chipsets, there are several resources in the Intel chipsets that are not automatically recognized by some Microsoft Windows operating systems. It is critical that the INF utility is installed in order to optimize platform performance with Intel Pentium 4 processor-based systems using Microsoft Windows XP. It is also critical that the INF utility is installed first before any other drivers.

Install Latest Drivers
Updated drivers may include compatibility fixes and/or optimizations for Hyper-Threading Technology. Download and install the latest drives from the vendor's web site.

Verifying Hyper-Threading Technology in Windows* XP
Determine whether Hyper-Threading Technology is enabled in Windows XP by viewing the Task Manager's CPU history graph or Device Manager.

Verifying Hyper-Threading Technology using Windows XP's Task Manager
Hyper-Threading Technology is enabled if there are two CPU usage history graphs within Windows XP Task Manager. If only one CPU graph is displayed and Hyper-Threading Technology is enabled in the BIOS settings, then make sure Microsoft Windows XP Service Pack 1 (or higher) is properly installed. Only one CPU history graph will be displayed in Task Manager if Hyper-Threading Technology is disabled in the BIOS settings.

Follow these steps, to verify Hyper-Threading Technology is enabled in Windows XP Task Manager:

1. Right click Task Bar
2. Click Task Manager
3. Click the Performance tab

Note: It is important to have the latest INF utility in order to optimize platform performance with Intel Pentium 4 processor-based systems using Microsoft Windows XP.

Follow these steps, to verify Hyper-Threading Technology is enabled in Windows XP Device Manager:

1. Click Start Menu
2. Click Control Panel
3. Double click System
4. Click the Hardware tab
5. Click Device Manager
6. Double click Processors

• Hyper-Threading Technology Home Page, for white papers and presentations:
  http://developer.intel.com/technology/hyperthread/
• IA-32 Intel® Architecture Software Developer's Manuals: http://developer.intel.com/design/Pentium4/manuals/
• Software Technologies, Hyper-Threading Technology: http://www.intel.com/cd/ids/developer/asmo-na/eng/technologies/threading/hyperthreading/index.htm
  
• More information on the Pentium® 4 processor is available on the Intel web site.
  
  ^†Hyper-Threading Technology requires a computer system with an Intel® Pentium® 4 processor supporting Hyper-Threading Technology and a Hyper-Threading Technology enabled chipset, BIOS and operating system. Performance will vary depending on the specific hardware and software you use.

This applies to:

Intel® Pentium® 4 Processors