BIOS Time vs PC Time.


Mitch

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Windows 11 Home
Hi, In the UK at least, the clocks go forward 1 hour at the end of this month for DST/BST. In October last year we had our PC's set to automatically adjust for the clock changes when the clocks go back 1 hour,, however this didn't happen and the PC time was 1 hour out - this happened our our 4 PC's. I synced the time to the internet clock and it was adjusted correctly. I also checked the time in the BIOS and it was still 1 hour out so I changed it manually. My question is, are the PC and BIOS times controlled and adjusted separately or are they linked, and if so, which one changes the other? At the moment, the "Adjust for clock changes" box is unchecked due to last year's problem but would like to have the time change done automatically. Would be grateful for advice. Thanks.
 

My Computer

System One

  • OS
    Windows 11 Home
We change Sunday morning but I do it before bed Saturday night. The issue with the BIOS is it is not the operating system, doesn't go out on the Internet so the time does have to be changed manually. What the OS does is change itself by the adjustment needed so that setting for the OS to make change should be set to do it. The BIOS won't change and when reverting to regular time the OS should also take care of it. When saving a file the date and time are written by the OS as to what it sees at that instant. Basically the BIOS provides information the OS reads to know how to run things, pretty much a reference point.
 

My Computers

System One System Two

  • OS
    Win11 Pro RTM
    Computer type
    Laptop
    Manufacturer/Model
    Dell Vostro 3400
    CPU
    Intel Core i5 11th Gen. 2.40GHz
    Memory
    12GB
    Hard Drives
    256GB SSD NVMe
  • Operating System
    Windows 11 Pro RTM x64
    Computer type
    PC/Desktop
    Manufacturer/Model
    Dell Vostro 5890
    CPU
    Intel Core i5 10th Gen. 2.90GHz
    Memory
    16GB
    Graphics card(s)
    Onboard, no VGA, using a DisplayPort-to-VGA adapter
    Monitor(s) Displays
    24" Dell
    Hard Drives
    512GB SSD NVMe, 2TB WDC HDD
    Browser
    Firefox, Edge
    Antivirus
    Windows Defender/Microsoft Security
Hi Berton, I'll check the "Automatically Adjust Time" box now for all our PC's and hopefully the PC time should show correctly after the clocks change, but if the BIOS time is still 1 hour behind, should I change it manually or leave it as is? Would there be any issues with the PC time being 1 hour ahead of the BIOS time? Thanks again.
 

My Computer

System One

  • OS
    Windows 11 Home
The "Bios" time should automatically be adjusted when the OS updates. Bios time and PC time "should" under normal circumstances be the same. For instance when you first power on a motherboard(motherboard, cpu, memory, etc) the bios time will be at whatever default setting is from last power on cycle. When a new OS is installed, without internet connectivity, the OS will use the Bios time as the System/OS time.

With Win7 during the install process you had an option to set the Time Zone however with Win10/11 the Time Zone defaults to Pacific time, which is stupid IMO. The OS install will update the motherboard RTC to whatever the OS chooses time zone wise. You can then have the OS set to check for proper time and update itself.

If for some reason your motherboard RTC drifts quite a bit when powered down and the system remains powered down for "some" period of time when you power on/boot the system the OS will initially pick up on the Bios time during bootup. If the OS does not check for current internet time the PC time will simply use the Bios time it detected during the power on/bootup process.
 

My Computer

System One

  • OS
    Win 7/10/11
    Computer type
    PC/Desktop
    Other Info
    I'm a computer enthusiast so have quite a few systems that I run. More like an advanced hobby.
I think what I'll do is have the PC Time checkbox to auto adjust for DST ticked and check again a day or two later to see if the BIOS time has changed to the correct time. Thanks again.
 

My Computer

System One

  • OS
    Windows 11 Home
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