# Dual Threaded CPU **URL:** \ **Category:** Factual Questions\ **Created:** [July 31, 2005, 5:11pm UTC](https://boards.straightdope.com/t/dual-threaded-cpu/315021 "2005-07-31T17:11:05Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![Nobody](https://avatars.discourse-cdn.com/v4/letter/n/94ad74/32.png) [@Nobody](https://boards.straightdope.com/u/Nobody)\ **Post date:** [July 31, 2005, 5:11pm UTC](https://boards.straightdope.com/t/dual-threaded-cpu/315021/1 "2005-07-31T17:11:05Z")
I use Windows XP Home Edition. If I were to buy and install a dual threaded CPU (after upgrading my motherboard, of course) would my version of XP, or any version of XP for that matter, be able to take advantage of the chip to give me faster speeds, or would it just seem like a normal CPU to me? Or does an OS even need to take advantage? For example, if I bought a dual socket motherboard, I’m pretty sure I’d need Windows Server 2003. Anyway, I’ve tried looking this up, and have had a very, very, hard time finding any answers, which is why I now turn to you. Thank you. ---
**Author:** ![Nanoda](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Nanoda](https://boards.straightdope.com/u/Nanoda)\ **Post date:** [July 31, 2005, 6:58pm UTC](https://boards.straightdope.com/t/dual-threaded-cpu/315021/2 "2005-07-31T18:58:56Z")
Are you talking Microsoft policy or visible improvements? Microsoft (and to my knowledge every non-free OS vendor) [charges more $$$ per CPU](http://www.geek.com/news/geeknews/2001nov/bch20011119008935.htm). With the advent of [hyperthreading](http://en.wikipedia.org/wiki/Hyperthreading) CPUs such as the Intel Xeon (which as I understand appears as two CPUs to the OS), Microsoft declared they would charge only a single CPU licence for such systems. This was really the only way to go, as these chips were available to the regular consumer, and MS couldn’t make the cost of the OS prohibitive. With multi-core CPUs (which function much more as two CPUs) being brought to market by both Intel and AMD, I recall reading someplace I can’t cite that they would similarly charge only for 1 CPU. As an aside, I have a dual Xeon machine where each CPU is hyperthreaded, and you can display useage graphs for 4 cpus. The Windows licence for it is a 2-CPU one. Oh, and this machine runs Windows 2000. XP Professional also supports multiple CPUs, though XP Home does not. ---
**Author:** ![Nobody](https://avatars.discourse-cdn.com/v4/letter/n/94ad74/32.png) [@Nobody](https://boards.straightdope.com/u/Nobody)\ **Post date:** [July 31, 2005, 7:13pm UTC](https://boards.straightdope.com/t/dual-threaded-cpu/315021/3 "2005-07-31T19:13:07Z")
> [@Nanoda](#): > > XP Professional also supports multiple CPUs, though XP Home does not. Whether or not XP home edition would support the dual threaded CPU is what I was asking about. Your answer indicates that I would need to upgrade to XP professional before I could get the full benefits of a dual threaded CPU. Thanks. ---
**Author:** ![jsmith](https://avatars.discourse-cdn.com/v4/letter/j/df705f/32.png) [@jsmith](https://boards.straightdope.com/u/jsmith)\ **Post date:** [July 31, 2005, 10:36pm UTC](https://boards.straightdope.com/t/dual-threaded-cpu/315021/4 "2005-07-31T22:36:13Z")
OK, I am confused here. Are we talking about a dual threaded CPU like Intel’s hyperthreading, A dual core cpu, or two CPUs (A dual socket motherboard is mentioned in the OP). Dual threaded CPUs (like Intel’s hyperthreading) are supported equally in XP home and pro. Cite: [http://support.microsoft.com/default.aspx?scid=kb;en-us;810231](http://support.microsoft.com/default.aspx?scid=kb;en-us;810231) I personally use a hyperthreaded processor under XP pro. It doesn’t seem much faster than a non-hyperthreaded processor in the same machine. The performance difference I see is that I am able to run more programs simultaneously and the times when my computer grinds away slowly processing something or a rogue application goes to 100% cpu usage (at the most it is 50% since it is contained to a single thread) are almost non-existent. ---
**Author:** ![Mr.Slant](https://avatars.discourse-cdn.com/v4/letter/m/c57346/32.png) [@Mr.Slant](https://boards.straightdope.com/u/Mr.Slant)\ **Post date:** [August 1, 2005, 12:50am UTC](https://boards.straightdope.com/t/dual-threaded-cpu/315021/5 "2005-08-01T00:50:39Z")
> [@Master Control](#): > > Whether or not XP home edition would support the dual threaded CPU is what I was asking about. Your answer indicates that I would need to upgrade to XP professional before I could get the full benefits of a dual threaded CPU. Thanks. I seem to remember that Microsoft does not consider “upgrading to Pro” to be a supported upgrade. I may be remembering wrong, but I strongly suspect you’d need to do either a format & reinstall or at least a reinstall to begin using Pro when you’d been using Home beforehand. ---
**Author:** ![jsmith](https://avatars.discourse-cdn.com/v4/letter/j/df705f/32.png) [@jsmith](https://boards.straightdope.com/u/jsmith)\ **Post date:** [August 1, 2005, 4:12am UTC](https://boards.straightdope.com/t/dual-threaded-cpu/315021/6 "2005-08-01T04:12:24Z")
You may upgrade from XP Home to Pro and even retain all your programs, settings, and files. I have done this on several machines without any problems. For example, our CFO got a good deal on a laptop with XP home edition but he couldn’t join our domain. He had to spend an additional $150 for an XP upgrade which was still a better deal than buying the same laptop from Sony with XP pro preinstalled. Companies like Sony and Dell “target” business users with higher prices. [http://www.microsoft.com/windowsxp/pro/upgrading/matrix.mspx](http://www.microsoft.com/windowsxp/pro/upgrading/matrix.mspx) ---
**Author:** ![Aestivalis](https://avatars.discourse-cdn.com/v4/letter/a/d6d6ee/32.png) [@Aestivalis](https://boards.straightdope.com/u/Aestivalis)\ **Post date:** [August 1, 2005, 4:12am UTC](https://boards.straightdope.com/t/dual-threaded-cpu/315021/7 "2005-08-01T04:12:38Z")
> [@Nanoda](#): > > Microsoft (and to my knowledge every non-free OS vendor) [charges more $$$ per CPU](http://www.geek.com/news/geeknews/2001nov/bch20011119008935.htm). With the advent of [hyperthreading](http://en.wikipedia.org/wiki/Hyperthreading) CPUs such as the Intel Xeon (which as I understand appears as two CPUs to the OS), Microsoft declared they would charge only a single CPU licence for such systems. Nanoda, that link is pretty old and your interpretation is not quite accurate. Microsoft is not charging more $$$ per CPU for the same operating system, but the different operating systems they sell at different price points have different levels of SMP support. Windows 2000 Professional = 2 CPUs (if you have 2 hyperthreaded CPUs, it will ignore hyperthreading on each CPU) Windows 2000 Server = 4 CPUs (if you have 4 hyperthreaded CPUs, it will ignore hyperthreading on each CPU) Windows XP Home = 1 CPU (single-core or hyperthreaded) It will ignore the second core on a dual-core CPU. Windows XP Professional = 2 CPUs (single-core, hyperthreaded or dual-core) Windows Server 2003 Standard = 4 CPUs (single-core, hyperthreaded or dual-core) Where you may be confusing the issue is with some non-OS software. MS SQL Server and Oracle have per-processor licensing available, and while they should in theory consider a hyper-threaded processor to be one processor, a dual-core processor will be considered two processors for licensing purposes. ---
**Author:** ![Nobody](https://avatars.discourse-cdn.com/v4/letter/n/94ad74/32.png) [@Nobody](https://boards.straightdope.com/u/Nobody)\ **Post date:** [August 1, 2005, 4:41am UTC](https://boards.straightdope.com/t/dual-threaded-cpu/315021/8 "2005-08-01T04:41:35Z")
> [@jsmith](#): > > OK, I am confused here. Are we talking about a dual threaded CPU like Intel’s hyperthreading, A dual core cpu, or two CPUs (A dual socket motherboard is mentioned in the OP). Sorry for the confusion, I was talking aobut dual threaded CPUs, not dual core or two CPUs. ---
**Author:** ![Nanoda](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Nanoda](https://boards.straightdope.com/u/Nanoda)\ **Post date:** [August 1, 2005, 4:47am UTC](https://boards.straightdope.com/t/dual-threaded-cpu/315021/9 "2005-08-01T04:47:44Z")
Gah - I was in a hurry with my post, I knew I’d get screwed up. As **jsmith** cites, XP Home _will_ support a single hyperthreaded CPU - Microsoft’s [usual decision](http://www.microsoft.com/licensing/highlights/multicore.mspx) is to have their base OS support a single hardware CPU. I find the info **Aestivalis** posts to be quite surprising though - the CPU restrictions seem somewhat excessive. BTW, if you use a dual-CPU board or hyperthreaded CPU, make sure that you enable support for them in the BIOS. I bought my dual-CPU box used, and noticed that hyperthreading was disabled in the BIOS. Turning it on made two virtual CPUs magically appear. 🙂 ---
**Author:** ![Askance](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/askance/32/8281_2.png) [@Askance](https://boards.straightdope.com/u/Askance)\ **Post date:** [August 1, 2005, 4:51am UTC](https://boards.straightdope.com/t/dual-threaded-cpu/315021/10 "2005-08-01T04:51:12Z")
[Hyperthreading](http://www.novell.com/coolsolutions/feature/637.html) is not going to bring you any increase in performance, unless you spend your time doing CAD/CAM work or similar. > [@](#): > > Hyper-Threading will increase the latency of individual requests and trade that for increased throughput; any individual request takes longer to complete, but more requests can be completed in a given time period. Going from uni-processor to multi-processor also adds cache contention and the increased locking complexity also slows things down; so performance will vary depending on what you are doing. You end up with two virtual processors running at around 65% the speed of a stand-alone processor. If you add the two together you get 130%. > > Therefore, if the workload doesn’t max out a uniprocessor system, you wouldn’t want to add latency to each individual request (i.e. by turning on Hyper-Threading) just so you can increase the throughput - because your current throughput capacity is more than sufficient for the workload. Hyper-Threading should be used to increase throughput in servers that are maxed out. ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [August 1, 2005, 7:37am UTC](https://boards.straightdope.com/t/dual-threaded-cpu/315021/11 "2005-08-01T07:37:07Z")
A similar question came up during the XP64 Beta. I’m not sure if **Aestivalis** is quite correct. Windows NT and 2000 do not ignore hyperthreading - they see the HT as a second CPU. This I’ve seen at work. XP Home will see only one CPU but will allow hyperthreading without seeing it as a second real CPU. It will ignore the second CPU on a dual-core CPU. XP Pro 32 bit will see two CPUs and will allow hyperthreading as XP Home. A dual-core processor counts as two CPUs. XP Pro 64 bit works off _sockets_, and allows a maximum of two sockets. Each socket can contain a single CPU, a hyperthreaded CPU, or a dual-core processor with two CPUs. ---
**Author:** ![RaftPeople](https://avatars.discourse-cdn.com/v4/letter/r/6f9a4e/32.png) [@RaftPeople](https://boards.straightdope.com/u/RaftPeople)\ **Post date:** [August 1, 2005, 7:56am UTC](https://boards.straightdope.com/t/dual-threaded-cpu/315021/12 "2005-08-01T07:56:27Z")
Something to keep in mind: Intel’s hyper-threading is merely a duplication of the registers so the CPU can more quickly switch between threads, but the execution of instructions is not handled by separate circuitry. That’s why you only get about a 15% boost from Intel’s hyper-threading. ---
**Author:** ![Ms2001](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ms2001/32/18463_2.png) [@Ms2001](https://boards.straightdope.com/u/Ms2001)\ **Post date:** [August 1, 2005, 8:57am UTC](https://boards.straightdope.com/t/dual-threaded-cpu/315021/13 "2005-08-01T08:57:34Z")
> [@RaftPeople](#): > > Something to keep in mind: > Intel’s hyper-threading is merely a duplication of the registers so the CPU can more quickly switch between threads, but the execution of instructions is not handled by separate circuitry. > > That’s why you only get about a 15% boost from Intel’s hyper-threading. Well, it’s not separate circuitry, but it does allow two threads to run at once. The CPU already has multiple units to do things like integer math, and it can execute two instructions simultaneously in the right circumstances (e.g. the inputs to one instruction don’t depend on the result of the other). HT, from what I understand, allows the CPU to look at two different threads for those instructions instead of having to take them from the same thread. ---
**Author:** ![ratatoskK](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ratatoskk/32/2987_2.png) [@ratatoskK](https://boards.straightdope.com/u/ratatoskK)\ **Post date:** [August 1, 2005, 3:30pm UTC](https://boards.straightdope.com/t/dual-threaded-cpu/315021/14 "2005-08-01T15:30:30Z")
You may want to consider the AMD Opteron if you’re serious about it. [http://www.amd.com/us-en/Processors/ProductInformation/0,,30\_118\_8825,00.html](http://www.amd.com/us-en/Processors/ProductInformation/0,,30_118_8825,00.html) [http://www.tomshardware.com/cpu/20030422/opteron-02.html](http://www.tomshardware.com/cpu/20030422/opteron-02.html) [http://www6.tomshardware.com/business/20050330/multicores-02.html](http://www6.tomshardware.com/business/20050330/multicores-02.html) [http://www6.tomshardware.com/business/20050331/index.html](http://www6.tomshardware.com/business/20050331/index.html) ---
**Author:** ![Mr.Slant](https://avatars.discourse-cdn.com/v4/letter/m/c57346/32.png) [@Mr.Slant](https://boards.straightdope.com/u/Mr.Slant)\ **Post date:** [August 1, 2005, 4:18pm UTC](https://boards.straightdope.com/t/dual-threaded-cpu/315021/15 "2005-08-01T16:18:42Z")
> [@jsmith](#): > > You may upgrade from XP Home to Pro and even retain all your programs, settings, and files. > > SNIP My bad. I was probably thinking of Win 2K Pro upgrades to XP Home.