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It has been superseded by a 13 later edition-lt ed By 14 Joe Pranevich (Before we begin, I am still missing information on video4linux, SCSI, sound, ftape, and other subsystems. If you know something that I didn't include, please let me know. I can barely keep up with the kernel traffic and reading patches as-is; In the Linux world, it is uncommon to announce release dates; Before we move into the meat and bones of the situation, I always like to step back for a moment and say a few things. No longer would just obscure computer publications trumpet the latest and greatest from the Linux worl, but mainstream publications as well. With the attention has come the inevitable FUD (Fear, Uncertainty, and Doubt) that we prayed would never come, but out of this media molasses we have emerged as a stronger community. While many of Linux's weak points were trumpeted and many members of the Linux community despaired, there were still the legions of kernel hackers that worked day and night to take those weaknesses, acknowledge them, and work to fix them. I do ask however that you cite the source whenever possible (both myself and the community who made this document possible) and if you require any clarifications, please do not hesitate to email me at the addresses below with your questions. If you would like to reprint or translate this article in full or in part in any medium, please email me at the address below so that I can be aware of your work before you do so. I will make a list of translations that I am aware of available. This is still a draft document and may not be 100% accurate. Also, new subsections have been added based on comments I received. I may keep or removed them later depending on user input. Some of these subsections will become full-blown articles at some point in the future. We all have different notions of what changes are important, if I don't mention a particular update that you feel is important, by all means please let me know. However now that a feature freeze has been announced, it is likely that we will soon have the first "final" draft in approximately three weeks give or take a couple years. Other than the email, I'm in no way associated with nor speak for Linux Today. This work also has absolutely nothing to do with Lycos, my employer. The views here are all mine and this article does not constitute an endorsement from Lycos or any other such thing. They are however a pretty damn fine company to work for. Just as the kernel is the heart of the Linux (or GNU/Linux or whatever) Operating System, the kernel itself can be divided into core and non-core parts. Linux is much more than just a collection of assorted device drivers, as any operating system must be. It's what binds these drivers together into a cohesive unit that matters. It's the scheduler, the resource allocator, the virtual filesystem layer, memory management, and so many other unsung features that are the real heroes of the Linux world. These are the portions of the Linux operating system that really define what is Linux because on every platform that Linux has been ported to from i386 (Intel-compatible PC), to ARM (embedded devices), to Sparc64 (high-end servers) this code is the same. Unfortunately it was deficient in a number of important ways which proved crucial to the needs of a modern desktop operating system. Additionally, this has laid the groundwork for ISA PnP support which is discussed more fully later in this article. The virtual filesystem layer (VFS) has also been heavily modified from earlier Linuxes. As you can imagine, this made things very complicated as the kernel developers had to code with kid gloves to always ensure that these caches were in synch when they had to be. During the course of this rewrite, many race conditions (errors caused when multiple processes "race" for access to unprotected variables) were removed and the code streamlined to allow significantly better scaling to higher-end systems and disk writes to happen faster when multiple volumes are involved. With high-end systems with many thousands of users, this could become a problem very quickly. On high-end servers with as little as half a gigabyte of RAM installed, it is easily possible to support as many as 16 thousand processes at once. Other users have reported being able to run many more than that on their specific systems. This was one of the major bottlenecks that kept Linux out of the Enterprise markets. Some subsystems have been added or expanded and some have been streamlined. This additional RAM will not be treated in exactly the same way as lower RAM (due to Intel design features) but will however be used by many in-kernel structures. Binary Types One often overlooked portion of the Linux kernel is the program loader; When a java application was executed, the Java binary loader would load up your Java interpreter with the proper arguments. Many types of drivers will become more "plug and play" (if I me be so bold as to abuse that term) as they will be initialized based on how they are linked rather than by having an explicit initialization line in the core code. The Many Flavors of Linux While infrastructure is the heart of the Linux operating system, it is the parts of the operating system that are specific to the individual flavors of Linux that are most obvious to the end users. These "arms and legs" of the Linux operating system include all of the architecture dependent and independent driver code which control the processors, disk drives, ports, and everything else that provides real access to the computer. For the purposes of this article, I will be concentrating on i386 Linux because it is the flavor that I am most familiar. This includes optimizations for 386, 486, 586 (Pentium), and 686 (Pentium Pro / Pentium II / Pentium III) processors, as well as "compatible" counterparts such as those made by AMD and Cyrix. To my knowledge, the only multi-processor systems which we still do not completely support are some very old 486 ones that mix 486DX and 486SX chips in the same system. This is mainly because the SX chips did not contain math coprocessors and there is some difficulty in making sure that applications that need floating point math get to work on the right one. As you can imagine, there isn't much call for this feature. This porting process is no doubt simplified by Linux's existing support for 64-bit processors (including Compaq's Alpha chips and the Sparc64) which are already merged into the main Linux tree. However a vast majority of the difficult and subtle parts are completed and all that remains are problems derived from a legacy world. The answer, at least right now, is that there is no such animal. A sister project, ELKS (Embeddable Linux Kernel Subset) is working to make a Linux-like operating system run on these machines, including protected mode support for chips that support it. This project is separate from Linux-proper however and is outside the scope of this document. Processors however are just a small part of the guts of a computer. Equally important to its operation is its bus architecture, the component of the system that is responsible for (or irresponsible towards, as the case may be) internal and external devices. The biggest news in this area is that ISA PnP, the somewhat misguided attempt to support device configuration and detection on the ISA bus, is finally supported at the kernel level! In the future, this will allow PnP devices to "just work" and not need any supplementary configuration utilities to function properly. Universal Serial Bus, a new external bus type just now coming into prominence for devices such as keyboards, mice, sound systems, and scanners is now supported in the Linux kernel. At the time of this writing, the support is not 100% and many individual and common USB devices are not supported or not completely supported. I would be confident however that the number of devices which are supported will only rise over time, just as we observed a similar rise in the number of framebuffer devices that are now supported. Other devices, such as modems and network cards, already have preliminary suppo...
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