These realizations led to a series of second generation microkernels, which further reduced the complexity of the system and placed almost all functionality in the user space. For instance, the L4 kernel (version 2) includes only seven system calls and uses 12k of memory, whereas Mach 3 includes about 140 functions and uses about 330k of memory. IPC calls under L4 on a 486DX-50 take only 5μs, faster than a UNIX syscall on the same system, and over 20 times as fast as Mach. Of course this ignores the fact that L4 is not handling permissioning or security; but by leaving this to the user-space programs, they can select as much or as little overhead as they require.
These realizations led to a series of second generation microkernels, which further reduced the complexity of the system and placed almost all functionality in the user space. For instance, the L4 kernel (version 2) includes only seven system calls and uses 12k of memory whereas Mach 3 includes about 140 functions and uses about 330k of memory. IPC calls under L4 on a 486DX-50 take only 5μs, faster than a UNIX syscall on the same system, and over 20 times as fast as Mach. Of course this ignores the fact that L4 is not handling permissioning or security; but by leaving this to the user-space programs, they can select as much or as little overhead as they require