“Unix time” counts the seconds that have passed since 01/01/1970.
For example, in Windows, you can read the installation date from the Windows Registry, and the returned value is “Unix time”:
$values = Get-ItemProperty 'HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion' $installDateUnix = $values.InstallDate $installDateUnix
The result is a large number similar to this:
1601308412
To convert “Unix time” to a real DateTime value, .NET Framework provides a type called [DateTimeOffset]:
$values = Get-ItemProperty 'HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion' $installDateUnix = $values.InstallDate [DateTimeOffset]::FromUnixTimeSeconds($installDateUnix)
Now you get back different date and time representations:
DateTime : 28.09.2020 15:53:32 UtcDateTime : 28.09.2020 15:53:32 LocalDateTime : 28.09.2020 17:53:32 Date : 28.09.2020 00:00:00 Day : 28 DayOfWeek : Monday DayOfYear : 272 Hour : 15 Millisecond : 0 Minute : 53 Month : 9 Offset : 00:00:00 Second : 32 Ticks : 637369052120000000 UtcTicks : 637369052120000000 TimeOfDay : 15:53:32 Year : 2020
To get the installation time in local time, you could melt it all together in a one-liner:
PS> [DateTimeOffset]::FromUnixTimeSeconds((Get-ItemProperty 'HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion').InstallDate).DateTime Moday, September 28, 2020 15:53:32
