You could use WMI. The "table" Win32_LogicalDisk contains the desired information.

use Win32::OLE qw( in );

my $wmi_service = Win32::OLE->GetObject("winmgmts:{impersonationLevel=
+impersonate}!\\\\.\\root\\cimv2")
   or die("Unable to connect to WMI: $!\n");

# DriveType 3 = local hard disk
my $disk_col = $wmi_service->ExecQuery("
   SELECT DeviceID
     FROM Win32_LogicalDisk
    WHERE DriveType = 3
");

my @drives = map { $_->DeviceID } in $disk_col;

local $, = ", ";
local $\ = "\n";
print @drives;
[download]

On my computer, the above prints C:, D:, E:.
If I remove the WHERE clause, it prints A:, B:, C:, D:, E:, F:, G:, H: (Floppy drives, hard drives, optical drives, USB drives, network drives, virtual drives, etc.)