Intel® Hyper-Threading Technology: Your Questions Answered

By Shannon Cepeda (Intel) (16 posts) on June 2, 2009 at 2:33 pm

I have received a number of customer questions recently on Intel® Hyper-Threading Technology. Hyper-Threading Technology is available on the new Intel® Core™ i7 processor and the Xeon® 5500 series processors. Here are a few of my favorite questions and answers - ranging from the basics to more advanced topics.

What is it?
Intel® Hyper-Threading Technology is a performance feature on our new Intel® Core™ i7 processor and the Xeon® 5500 series processors. Put simply, it allows one core on the processor to appear like 2 cores to the operating system. This doubles the execution resources available to the O/S, which potentially increases the performance of your overall system. For the visually-oriented, you can view a graphical explanation of Intel® Hyper-Threading Technology by clicking on the demo here.

Talking about cores, threads, and Hyper-Threads can get a bit confusing. To make things simple for the rest of this blog, I'm going to call Hyper-Threads hardware threads, and O/S level threads software threads. Just as a refresher, a core is 1 CPU. Each Core™ i7 or Xeon® 5500 series processor shipping currently has 4 cores (we may offer other versions in the future).

How can I tell if my system is using Hyper-Threading Technology?
You must have a processor, chipset, operating system, and BIOS that all support the technology. Luckily, that is not much of a problem. Many of the desktop and server platforms that ship with Nehalem-based processors include this support. Most of these platforms will allow you to enable or disable Hyper-Threading Technology as a BIOS option (it should be enabled by default). You can view your CPU information using the Task Manager in Windows*, and /proc/cpuinfo in Linux*. If you have a supported platform and Hyper-Threading is enabled, you should see twice the number of CPUs as you have physical cores in your platform. For example, if you have a dual-processor Xeon® 5500 series server, you should see 16 CPUs. (16 hardware threads running on 8 physical cores, 2 threads per core.)


Available CPUs on the same platform with Hyper-Threading Technology disabled (top) and enabled (bottom).

Can I run 2 applications simultaneously on 2 different threads on the same core?
Yes. The 2 software threads running on a single core do not have to be threads of the same process. They could be (in the case of multi-threaded software), or they could be from 2 separate applications. Which 2 software threads would run on the 2 hardware threads of a Hyper-Threaded core would be up to the operating system. So, yes, you could have 2 different applications running on the same core at the same time. (Whether you would get equal performance in this scenario as you would with the 2 apps running on separate cores is a different issue – see question 6.)

Now that you know the basics, visit my article in the Intel Software Network knowledgebase to learn more. Get the answers to these 3 advanced questions on Intel® Hyper-Threading Technology:

• How is it implemented, under the covers?
• Can I give one hardware thread priority or ensure that it doesn’t get “starved” for execution time?
• What kind of performance benefit will I get from using Intel® Hyper-Threading Technology?

What other questions do you have on the performance features of the new Nehalem-based processors?

Categories: Parallel Programming
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Comments (5)

June 3, 2009 12:59 PM PDT


pier-olivier p.c.		 As I understand it simply saves 2 process context so it can switch between those 2 quickly. Am I right?
June 3, 2009 3:58 PM PDT

Shannon Cepeda (Intel)
Shannon Cepeda (Intel)Total Points:
3,823
Black Belt
 In a way. You could think of it like this, but with one important clarification: this happens at the hardware level. The pipeline recognizes 2 hardware thread contexts (per core) so that it can execute instructions from each. The operating system's management of process contexts is separate.
June 5, 2009 9:12 AM PDT

TC2009074
TC2009074
 http://www.intel.com/technology/product/demos/multi/demo.htm.....+body_demo

hyper-threading explained in simple terms
March 15, 2010 2:08 PM PDT


Edb2010		 That video demonstration is impressive to understand from the Processor point. How about bus speed and Ram. How do these fit into the Intel Extreme i7 Core with multiple software apps open?

Here is a scenario that utterly kills my time on my current unit. I have a Dell Precision 690 workstation with dual xeon processors (3.73 GHz) and 2 gig of RAM (Running 32 bit XP mode). I now open the following:

1. A 700 meg file in Photoshop
2. A 500 meg file in Illustrator
3. A 25 meg file in Quark.

My supervisor works in Real Time mode. Therefore, I need to bounce between these apps to generate a final piece of art. Unfortunately, something in the system does not like the bouncing around as Microsoft XP simply slows down the process to get the requests done. Sometimes I think the unit simply crashed but as I mention to my supervisor, please give it 5 minutes. In 5 minutes it gets out of a froze mode and the procedure is completed.


I just made a purchase on Dells new 6500 covet which I am hoping will do better than the Precision 690 because the entire system is upgraded (New hardware across the board for i7 support).

The new system I bought will max everything it has ... Extreme Core i7, 16 gigs of RAM, nvidia 3800FX (to eliminate screen refresh issues from the 690) but no solid state hard drive.
It will have 1333 bus speed though.

I'm curious if bouncing between these apps on the new system will not duplicate the situation of the Precision 690 running dual Xeon 3.73 GHz.

Any thoughts would be helpful.
April 26, 2010 9:28 AM PDT


Marv		 hi Edb2010,

w/ the specs you mention, you should be ok using those 3 programs at the same time. in your previous system those 2 gig of ram was killing your pc.

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