Q:

What languages are Windows, Mac OS X and Linux written in?

I was just wondering who knows what programming languages Windows, Mac OS X and Linux are made up from and what languages are used for each part of the OS (ie: Kernel, plug-in architecture, GUI components, etc).
I assume that there are multiple languages for each and obviously I know the Linux kernel is written in C.
I'm totally guessing here that Mac OS X contains a lot of Objective-C code as it is Apple's language derived from NeXT.
Windows, I have heard contains C, C++ and Intel Assembly. Do Linux or Mac OS contain any Assembly code?
Also, are there scripting languages like Ruby, Python, etc used by the OS developers for scripting parts of the OS? What parts of the OS would be written in each language?

A:

Windows: C++, kernel is in C
Mac: Objective C, kernel is in C (IO PnP subsystem is Embedded C++)
Linux: Most things are in C, many userland apps are in Python, KDE is all C++

All kernels will use some assembly code as well.

A:

Linux: C. Some parts in assembly.

[...] It's mostly in C, but most people wouldn't call what I write C.
It uses every conceivable feature of the 386 I could find, as it was
also a project to teach me about the 386. As already mentioned, it
uses a MMU, for both paging (not to disk yet) and segmentation. It's
the segmentation that makes it REALLY 386 dependent (every task has a
64Mb segment for code & data - max 64 tasks in 4Gb. Anybody who needs
more than 64Mb/task - tough cookies). [...] Some of my "C"-files
(specifically mm.c) are almost as much assembler as C. [...] Unlike
minix, I also happen to LIKE interrupts, so interrupts are handled
without trying to hide the reason behind them. (Source)

Mac OS X: Cocoa mostly in Objective-C. Kernel written in C, some parts in assembly.

Mac OS X, at the kernel layer, is mostly an older, free operating system called BSD (specifically, it’s Darwin, a sort of hybrid of BSD, Mach, and a few other things)... almost entirely C, with a bit of assembler thrown in. (Source)
Much of Cocoa is implemented in Objective-C, an object-oriented language that is compiled to run at incredible speed, yet employes a truly dynamic runtime making it uniquely flexible. Because Objective-C is a superset of C, it is easy to mix C and even C++ into your Cocoa applications.
(Source)

Windows: C, C++, C#. Some parts in assembler.

We use almost entirely C, C++, and C# for Windows. Some areas of code are hand tuned/hand written assembly. (Source)

Unix: C. Some parts in assembly. (Source)

A:

Mac OS X uses large amounts of C++ inside some libraries, but it isn't exposed as they're afraid of the ABI breaking.

