L4 microkernels are actually pretty widely deployed in cellular phone / tablet baseband processors (the real-time stack that actually handles communicating with

L4 microkernels are actually pretty widely deployed in cellular phone / tablet baseband processors (the real-time stack that actually handles communicating with the cell tower), including some iPad models. As far a cache, depending on what's going on, you may find lower cache usage. In school, I had an assignment to run a simulated filesystem benchmark and identify the sizes of various caches on my system from the benchmark results. I was quad-booting Linux, L4Linux, QNX, and Win2k on my desktop at the time, so I ran the benchmark on Linux, L4Linux, and QNX. QNX actually showed better cache utilization than Linux (bigger filesystem working sets before noticeable percentages of cache misses at the various levels). If your kernel is extremely small, it has good cache locality, likewise for a small fs driver. So, if you're really hammering just one application and one or two drivers, you might get better cache utilization from a microkernel.