Reading the installation date of the C# OS

Question

With the C# Core 3.1 WinForms application, the first installation date of the operating system cannot be read through regedit. It gives different results than the date given by "SystemInfo" command with CMD.

CMD "System Info":

CMD Image

Original Install Date: 11/26/2022, 1:08:26 PM

C# Read a "Regedit InstallDate(DWord)":

Regedit Image

Date: "1.01.1601 00:02:46"

C# Read a Date

RegistryKey key = RegistryKey.OpenRemoteBaseKey(RegistryHive.LocalMachine, computerName);
key = key.OpenSubKey(@"SOFTWARE\Microsoft\Windows NT\CurrentVersion", false);
if (key != null)
{
    DateTime installDate =
        DateTime.FromFileTimeUtc(
            Convert.ToInt64(
                key.GetValue("InstallDate").ToString()));

    return installDate;
}
return DateTime.MinValue;

Answer 1

The value in InstallDate is not a FILETIME value, but a Unix Time (seconds since 1970-01-01). You can use

var installDate = DateTimeOffset.FromUnixTimeSeconds(regValue);

to convert to a DateTimeOffset.

For other conversion methods see How do you convert epoch time in C#?