Preemption
The server kernel has kernel preemption turned off (CONFIG_PREEMPT_NONE=y), while the desktop kernel has it enabled (CONFIG_PREEMPT_BKL=y, CONFIG_PREEMPT_VOLUNTARY=y). Preemption works along with scheduling to fine-tune performance, efficiency and responsiveness. In non-preemptive kernels, kernel code runs until completion; the scheduler can't touch it until it's finished. But the Linux kernel allows tasks to be interrupted at nearly any point (but not when it is unsafe, which is a whole huge fascinating topic all by itself), so that tasks of lesser-priority can jump to the head of the line.
This is appropriate for desktop systems because users typically have several things going at once: writing documents, playing music, Web surfing, downloading and so on. Users don't care how responsive background applications are; they care only about the ones they're actively using. So if loading a Web page takes a little longer while the user is writing an e-mail, it's an acceptable trade-off. Overall efficiency and performance are actually reduced but not in a way that annoys the user.
On servers you want to minimize any and all performance hits, so turning off preemption is usually the best practice.
The disk's ITR rating and internal cache size can be critical when tuning maxcontig (maximum contiguous I/O size). Note: maxphys and maxcontig must be tuned at the same time. The unit of measurement for maxphys is bytes; maxcontig is in blocks. maxcontig can be changed via the mkfs, newfs or tunefs commands.
