1. Is your OS Windows 7, 8, or 10? Go to step 3. Is it XP, Vista, or similar? Go to step 2. Linux/Unix? Go to step 6.
    2. <li>Give C: 20 GB and put your data on D:</li>

<li>Do you love tinkering and reinstalling OSes for fun? Go to step 4. Otherwise, step 5.</li>

<li>Give C: 70 GB and put your data on D:</li>

<li>Just use a single partition — C: alone is enough.</li>

<li>Linux doesn't have partitions like C:. Give /boot a partition of 500 MB, create a swap partition the same size as your RAM, and throw everything else under /. Pick a filesystem: ext4, LVM, btrfs, or ZFS. LVM is the middle-of-the-road choice, ZFS can be a bit of a hassle, and btrfs compatibility is still not great — you may run into strange issues sometimes.</li>

Why partition at all? Back in the ancient days, operating systems weren't very stable, and you might need to reinstall the OS frequently. Each reinstall could wipe everything on the system drive, so keeping data on the system drive wasn't safe. And if you installed software on D:, you could often skip reinstalling much of it after a reinstall.

But starting with Windows 7, OS stability improved dramatically. Even if you accidentally (or deliberately) reinstall, you can keep your old data, and in the vast majority of cases you can still boot in and back up your data first. At this point, everyday experience matters most. Do you want to put things directly on the desktop? Is it annoying to switch back and forth between C: and D: to find things? Hassles like these caused by partitioning are actually unnecessary.

As for viruses and the like — buy a licensed copy of Windows. Actually, if you buy a branded PC it already comes with one, or you can just buy one yourself for next to nothing. Then use Windows' built-in antivirus. As long as you don't go out of your way to do something reckless, viruses really aren't a big problem these days. And as mentioned earlier, even if a virus does take your system down, you can boot into Safe Mode — or at the very worst, boot calmly from a PE environment and copy out the data you need.

There are still people who think XP is the best operating system in the world, mindlessly passing along outdated advice from who-knows-how-many years ago. Truly speechless.