# Windows Instance/Guest OS Time Skew

## Problem

The clock within a Windows-based instance is not in sync with the underlying hypervisor time.

## Solution

1. Edit the Boot Configuration Data (BCD) and set `USEPLATFORMCLOCK` to `on` .

{% tabs %}
{% tab title="Powershell" %}

```powershell
bcdedit /set USEPLATFORMCLOCK on
```

{% endtab %}
{% endtabs %}

2. Shutdown the instance, or perform a hard-reboot for the change to take effect.

## Additional Information

If the guest OS is reliant upon the timestamp counter (TSC), timing issues can, and have been documented to occur, as this is reliant upon the CPU, which can have skew in frequency, missed tickets, etc. which lead to time drift, comparative to the real-time clock (RTC).

If you've: a) added the required attribute, b) modified the boot-configuration data to leverage the RTC/system clock, and c) either shutdown, and re-started or hard-rebooted the instance – the change should've taken effect.

Outside of that, with regards to NTP – my recommendation was more along the lines of ensuring that the Windows guest OS synchronizes to a centralized time source itself, such that it isn't reliant upon any of the underlying system timers/clocks.


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