As ikegami rightly says, you should use the Switch module at your peril - all sorts of dangers lurk therein. You _could_ roll your own poor mans' switch:

SWITCH:
{
    $operatingsystem eq "170" && do {
        $Folder = "winvista";
        $Readme = "readme_winvista.txt";
        last SWITCH;
    };
       
    $operatingsystem eq "173" && do {
         $Folder = "winvista64";
         $Readme = "readme_winvista64.txt";
        last SWITCH;
    };

    $operatingsystem eq "119" && do {
        $Folder = "winvxp";
        $Readme = "readme_winxp.txt";
        last SWITCH;
    };

    $operatingsystem eq "210" && do {
        $Folder = "winxp64";
        $Readme = "readme_winxp64.txt";
        last SWITCH;
    };
    .
    .
    .
};
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But, as others have pointed out, the case (pun intended:-) for a hash in these circumstances is overwhelming.