Upgrading single CPU system to multi CPU system

Posted on 2006-03-19
Last Modified: 2012-08-13

I realise that when windows is installed, the installer selects a HAL based on the hardware it detects.

My question is, if I install a dual core CPU or add an additional CPU to a motherboard that only had *one* (non hyperthreaded) CPU, does the HAL automatically change from a uniprocessor hal to a multiprocessor HAL.

If not, what steps are required to get the OS using both CPU's/cores.

Geek in training

Question by:harrowc
    LVL 5

    Expert Comment

    Start up Windows, shut down all unnecessary programs and TSR’s and insert the installation CD.  Run the setup Program, select upgrade and that will upgrade the HAL to run both processors.
    LVL 23

    Accepted Solution

    From the windows support newsgroups (their answer was crisper than mine was going to be):

    You can add a processor to a Windows 2003 server/SBS 2003. Actually when we
    setup Win2003, we do have a choice to choose HAL to support single or dual
    CPU. However this is not recommended. When you choose to support dual
    processor while actually there is only 1 processor in the computer, you may
    experience many potential problems. The support method is to let system
    automatically choose the HAL when setting up Win2003 or SBS 2003. If you
    want to add another CPU, you can just power off the server, plug the other
    CPU and boot the system up. However there are two limitations:

    1. You should not change the motherboard.

    If you plan to upgrade to a dual CPU system, you should make sure your
    motherboard supports multiple CPU at the first time (make sure the Dell
    server hardware supports dual-CPU before setting up SBS 2003). If your
    motherboard does not support multiple CPU and you want to replace the
    motherboard when upgrading the system to a dual CPU system, you have to do
    a reinstallation (in-place upgrade) or even a clean installation.

    2. You should make sure the other CPU you plan to use is the SAME as the
    existing one in the computer.

    If you find that the other CPU is not recognized by Windows 2003
    automatically, you can use the information in the following article to
    manually upgrade to Multiprocessor PC:

    309283 HAL Options After Windows XP or Windows Server 2003 Setup

    More information:

    234558 HOW TO: Add Support for Multiple Processors in Windows 2000

    Please do not hesitate to let me know if you have any further concerns.

    I will look forward to hearing from you.

    Best regards,

    Crina Li (MSFT)

    Microsoft CSS Online Newsgroup Support

    Note:  I'm not Crina Li...but they deserve credit for their words.
    LVL 3

    Author Comment

    I believe juanfermin's answer would not work, I think windows setup would say something like: "you are already running this version of windows, you can't upgrade".

    To summarise TheCleaner's (copied) answer:
    It will just work if you are using 2003, just add or upgrade the CPU and Windows will be able to use it.
    If on 2000, do into device manager and change to the multiprocessor HAL first, then add the CPU.

    LVL 23

    Expert Comment

    You got it...thanks for the points.

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