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Re: E` un'ingiustizia ! Perché per Linux
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wow, sarà vero? farò atto di fede



BeOS è basato su un'architettura a microkernel



e quindi?http://www.oreilly.com/catalog/opensources/book/appa.htmlAppendix AThe Tanenbaum-Torvalds DebateWhat follows in this appendix are what are known in the community as the Tanenbaum/Linus "Linux is obsolete" debates. Andrew Tanenbaum is a well-respected researcher who has made a very good living thinking about operating systems and OS design. In early 1992, noticing the way that the Linux discussion had taken over the discussion in comp.os.minix, he decided it was time to comment on Linux.Although Andrew Tanenbaum has been derided for his heavy hand and misjudgements of the Linux kernel, such a reaction to Tanenbaum is unfair. When Linus himself heard that we were including this, he wanted to make sure that the world understood that he holds no animus towards Tanenbaum and in fact would not have sanctioned its inclusion if we had not been able to convince him that it would show the way the world was thinking about OS design at the time.We felt the inclusion of this appendix would give a good perspective on how things were when Linus was under pressure because he abandoned the idea of microkernels in academia. The first third of Linus' essay discusses this further.Electronic copies of this debate are available on the Web and are easily found through any search service. It's fun to read this and note who joined into the discussion; you see user-hacker Ken Thompson (one of the founders of Unix) and David Miller (who is a major Linux kernel hacker now), as well as many others.To put this discussion into perspective, when it occurred in 1992, the 386 was the dominating chip and the 486 had not come out on the market. Microsoft was still a small company selling DOS and Word for DOS. Lotus 123 ruled the spreadsheet space and WordPerfect the word processing market. DBASE was the dominant database vendor and many companies that are household names today--Netscape, Yahoo, Excite--simply did not exist.From: ast@cs.vu.nl (Andy Tanenbaum)Newsgroups: comp.os.minixSubject: LINUX is obsoleteDate: 29 Jan 92 12:12:50 GMT I was in the U.S. for a couple of weeks, so I haven't commented much onLINUX (not that I would have said much had I been around), but for what it is worth, I have a couple of comments now. As most of you know, for me MINIX is a hobby, something that I do in theevening when I get bored writing books and there are no major wars,revolutions, or senate hearings being televised live on CNN. My realjob is a professor and researcher in the area of operating systems. As a result of my occupation, I think I know a bit about where operatingare going in the next decade or so. Two aspects stand out: 1. MICROKERNEL VS MONOLITHIC SYSTEM Most older operating systems are monolithic, that is, the whole operating system is a single a.out file that runs in 'kernel mode.' This binary contains the process management, memory management, file system and the rest. Examples of such systems are UNIX, MS-DOS, VMS, MVS, OS/360, MULTICS, and many more. The alternative is a microkernel-based system, in which most of the OS runs as separate processes, mostly outside the kernel. They communicate by message passing. The kernel's job is to handle the message passing, interrupt handling, low-level process management, and possibly the I/O. Examples of this design are the RC4000, Amoeba, Chorus, Mach, and the not-yet-released Windows/NT. While I could go into a long story here about the relative merits of the two designs, suffice it to say that among the people who actually design operating systems, the debate is essentially over. Microkernels have won. The only real argument for monolithic systems was performance, and there is now enough evidence showing that microkernel systems can be just as fast as monolithic systems (e.g., Rick Rashid has published papers comparing Mach 3.0 to monolithic systems) that it is now all over but the shoutin'. MINIX is a microkernel-based system. The file system and memory management are separate processes, running outside the kernel. The I/O drivers are also separate processes (in the kernel, but only because the brain-dead nature of the Intel CPUs makes that difficult to do otherwise). LINUX is a monolithic style system. This is a giant step back into the 1970s. That is like taking an existing, working C program and rewriting it in BASIC. To me, writing a monolithic system in 1991 is a truly poor idea. 2. PORTABILITY Once upon a time there was the 4004 CPU. When it grew up it became an 8008. Then it underwent plastic surgery and became the 8080. It begat the 8086, which begat the 8088, which begat the 80286, which begat the 80386, which begat the 80486, and so on unto the N-th generation. In the meantime, RISC chips happened, and some of them are running at over 100 MIPS. Speeds of 200 MIPS and more are likely in the coming years. These things are not going to suddenly vanish. What is going to happen is that they will gradually take over from the 80x86 line. They will run old MS-DOS programs by interpreting the 80386 in software. (I even wrote my own IBM PC simulator in C, which you can get by FTP from ftp.cs.vu.nl = 192.31.231.42 in dir minix/simulator.) I think it is a gross error to design an OS for any specific architecture, since that is not going to be around all that long. MINIX was designed to be reasonably portable, and has been ported from the Intel line to the 680x0 (Atari, Amiga, Macintosh), SPARC, and NS32016. LINUX is tied fairly closely to the 80x86. Not the way to go. Don't get me wrong, I am not unhappy with LINUX. It will get all the peoplewho want to turn MINIX in BSD UNIX off my back. But in all honesty, I wouldsuggest that people who want a **MODERN** "free" OS look around for a microkernel-based, portable OS, like maybe GNU or something like that. Andy Tanenbaum (ast@cs.vu.nl) P.S. Just as a random aside, Amoeba has a UNIX emulator (running in userspace), but it is far from complete. If there are any people who wouldlike to work on that, please let me know. To run Amoeba you need a few 386s,one of which needs 16M, and all of which need the WD Ethernet card.