IDC is tipping Linux to overtake the Mac as the second most popular paid-for desktop operating system after Windows, reports ZD Net, though this should really be number 3 after Windows NT-based and DOS/Windows (which are entirely different operating sytems). The "paid for" note is important since IDC has no way of tracking how many copies of Linux are installed from downloads or by the re-use of paid-for software on multiple PCs. (Nor does it track the multiple pirate copies of Windows, of course. It's only with proprietary systems like the Mac that anyone has an accurate number.)