Linux:Kernel
From xbe wiki
The word "Linux" refers to the "Linux Kernel", which can be found at [1].
The kernel takes care of booting the system, load the supported hardware, optionally in form of driver modules (*.so). In Linux, all applications can communicate with the kernel through the pseudo-filesystem on /proc, the kernel also mantains all supported devices in the /dev structure.
The most visible advantage for the user (apart from performance) when using a Linux kernel is the flexibility. As linux user can specifically exclude or include given features from the kernel. If the user doesn't need soundcard support, the user just excludes that from the kernel, the same can be done with every device support. This leads to an optimized "heart of the system" which is fully customized to meet the needed requirements.
In Windows, the kernel cannot be recreated by the user and carries a lot of (mostly) unnused drivers, which wastes ressources and leads to a slower system as it could be.