The Synthesis operating system kernel combines several techniques to provide high performa.nce, incl1iding kernel code synthesis, fine-gra.in scheduling. and optimistic sylicllroliiza,tioii. Kernel code synthesis reduces the execution path for frequently used kernel calls. Optimistic synchronization increases concurrency within the kernel. Their combination results in significant performance improvement over tra.dit,ional operating system implementations. Using hardware and software emulating a. SUN 3/100 running SUNOS, Synt,hesis achieves several times to several dozen t.imes speedup for UNIX kernel calls and context switch times of 21 microseconds or faster.