What is the recommended boot partition size for Windows 7?

I've done half a dozen Windows 7 installs this week and the "base" install takes nearly 20 GB in my experience. I'm writing post this on my new Windows 7 Ultimate rig. I've installed literally nothing but drivers and 20 GB is used up already on my OS partition.

This is also confirmed by the Windows 7 System Requirements, which also lists that you need 20 GB at least to run Windows 7. So, I would recommend you to use at least 60 GB and to install your applications in a separate data partition.

Note that your system partition tends to grow over time due to updates, temporary files, logs and that kind of things; so, to anticipate this you would need sufficient space. If you look at other answers, you will see that some people have 40 or 50 GB so choosing 60 GB makes sure that you don't hit the border yet.

Given the hard disk sizes nowadays, 10 - 20 GB more shouldn't hurt. Unless you run a SSD...

I gave Windows 7 a 100 GB partition on a 1 TB drive, and according to the Windows Experience Index (WEI) I got a 7.2 for the drive. It's substantially better than using the whole 1 TB, which was more in the 5.9-6.0 range.

I read it has to do with the efficiency of having the OS partition first (outer-most part of the platters on the HDD), and that a smaller partition is more efficient. Believe me, there was a discernable improvement.

In a related question, Windows 7's base install was reported as weighing in at about 6 GB, compared to about 1.5 GB for a Windows XP install.

I've gotten by pretty well with a 20 GB partition for Windows XP, but I've been installing the big applications (games) to a separate drive. I estimate 40 GB should be all you'd need for a Windows 7 system partition.