The story goes that Andrew Tannenbaum (Comp Sci professor and creator of MINIX, which few can dispute was an inspiration for Linux) criticized Linux as "out of date", being monolithic. The Linux crowd, of course, was so delighted to have a kernel that WORKED and that was UNCONSTRAINED (MINIX is not GPL) that they did not let this deter them. (HURD was unheard of and Mach remains mockingly daunting.)
AIX/ESA, which reportedly sold only a handful of licenses and was withdrawn, had a "microkernel", and was ellegedly based on Mach. Sweet! It supposedly would let your 3090 sing! Fully exploited ESA hardware. (This is before they called it S/390.) But no one bought it. So you have a "monolithic" kernel which has succeeded and a modularized kernel which has failed. Most who know the theory behind them would tell you that the modular/micro kernel is better. In fact, both CP (VM) and MVS (z/OS) have substantial microkernel concepts in their nucleii these days. But it takes work. Given the loadable module support in Linux, one could almost call it "modular". (I can hear Alan Cox now!) Perhaps it will evolve into more of what the microkernel purists would demand. I hope so! Even now, it is a far cry from the truly monolithic thing it once was. -- RMT
