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-
All kernels will use some assembly code as well.
I have read or heard that Mac OS X is written mostly in Objective-C with some of the lower level parts, such as the kernel, and hardware device drivers written in C. I believe that Apple "eat(s) its own dog food", meaning that they write Mac OS X using their own Xcode Developer Tools. The GCC(GNU Compiler Collection) compiler-linker is the unix command line tool that xCode used for most of its compiling and/or linking of executables. Among other possible languages, I know GCC compiles source code from the C, Objective-C, C++ and Objective-C++ languages.
The Linux kernel is mostly written in C (and a bit of assembly language, I'd imagine), but some of the important userspace utilities (programs) are shell scripts written in the Bash scripting language. Beyond that, it's sort of hard to define "Linux" since you basically build a Linux system by picking bits and pieces you want and putting them together, and depending on what an individual Linux user wants, you can get pretty much any language involved. (As Paul said, Python and C++ play important roles)
As an addition about the core of Mac OS X, Finder had not been written in Objective-C prior to Snow Leopard. In Snow Leopard it was written in Cocoa, Objective-C
Mac OS X uses large amounts of C++ inside some libraries, but it isn't exposed as they're afraid of the ABI breaking.