How to access the 64-bit registry from a 32-bit Powershell instance?

If the enviroment variable PROCESSOR_ARCHITEW6432 exists and has the value AMD64 then you are running 32bit on a 64bit machine. Than you have to run the powershell in the virtual 64bit path %windir%\sysnative.

if ($env:PROCESSOR_ARCHITEW6432 -eq "AMD64") {
    write-warning "changing from 32bit to 64bit PowerShell..."
    $powershell=$PSHOME.tolower().replace("syswow64","sysnative").replace("system32","sysnative")

    if ($myInvocation.Line) {
        &"$powershell\powershell.exe" -NonInteractive -NoProfile $myInvocation.Line
    } else {
        &"$powershell\powershell.exe" -NonInteractive -NoProfile -file "$($myInvocation.InvocationName)" $args
    }

    exit $lastexitcode
}

When Powershell is running as a 32 bit process, I am not aware of a mechanism to "switch it" to 64bit mode. The whole point of virtualization support in 64bit systems is to make 32bit processes believe they are living in a 32bit OS...

However, that said I used the following technique in the past and it worked very nicely for me (the following code was tested on Vista SP1 x64 with Powershell v1). The technique relies on the fact that .NET's "Any CPU" executables will run as 64bit process even when invoked from a 32bit process. The steps we will be performing:

1. Compile a short C# program that will start powershell (i.e. a very simple "fork" implementation :-) )
2. Run the compiled C# program
3. The compiled C# program will start Powershell, but because it's "Any CPU", it will be running as a 64bit process so it will start 64bit Powershell (note that because this is just a proof-of-concept, I expect powershell to be in your 'path')
4. The new 64bit Powershell will run a commandlet of our choice

This is a screenshot of the above in action (notice bit-ness of the processes): Process tree http://img3.imageshack.us/img3/3248/powershellfork.png

The following program expects all the files listed to reside in the same directory. I recommend creating a test directory, e.g. C:\Temp\PowershellTest, and storing all the files there).

Entry point to the program will be a simple commandlet:

# file "test.ps1"
$basePath = Split-Path -resolve $myInvocation.MyCommand.Path
$exe = Join-Path $basePath test.exe
&"$env:SystemRoot\Microsoft.NET\Framework\v3.5\csc.exe" /nologo /target:exe /out:$exe (Join-Path $basePath test.cs)
&$exe (Join-Path $basePath visibility.ps1)

It runs csc (32bit, but it doesn't matter :-) ) and then runs result of csc compiler, passing one argument, (full path to) visibility.ps1 (this is the commandlet we want to run in 64bit Powershell).

The C# code is very simple as well:

// file "test.cs"
using System.Diagnostics;
static class Program {
    static int Main(string[] args) {
        ProcessStartInfo i = new ProcessStartInfo("powershell", args[0]);
        i.UseShellExecute = false;
        using(Process p = Process.Start(i)) {
            p.WaitForExit();
            return p.ExitCode;
        }
    }
}

And finally, your "visibility" script:

# file "visibility.ps1"
(dir HKLM:\SOFTWARE).count - (dir HKLM:\SOFTWARE\wow6432node).count

Running the entry script from 32bit Powershell now yields desired result (just to show I was not cheating I run the visibility script directly first, then using our fork technique):

Program run http://img3.imageshack.us/img3/2766/powershellrunc.png

With .NET API you can read 64-bit values like this:

$key = [Microsoft.Win32.RegistryKey]::OpenBaseKey([Microsoft.Win32.RegistryHive]::LocalMachine, [Microsoft.Win32.RegistryView]::Registry64)
$subKey =  $key.OpenSubKey("SOFTWARE\Microsoft\.NETFramework")
$root = $subKey.GetValue("InstallRoot")

I believe the built in cmdlet Start-Job will allow you to check the 64 bit registry from a 32-bit instance.

If not, using Invoke-Command to loop back to the local machine wil. A 64-bit machine will have two endpoints (64-bit and 32-bit), and the 64-bit endpoint will be the default.

Example creating a registry value and ensuring it is in the 64-bit path, not 32.

Invoke-Command -scriptblock {
    New-ItemProperty -Path HKLM:\SOFTWARE\Acme 
                     -Name NameofNewReg 
                     -PropertyType String -Value "1"
    } -computername .