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+
+ SOS: A Simple Operating System
+
+
+This is SOS, a Simple Operating System for i386-family
+processors. This is as simple as possible to show a way to program a
+basic Operating System on real common hardware (PC). The code should
+be easily readable and understandable thanks to frequent comments, and
+references to external documentation. We chose to implement the basic
+features of an OS, thus making design decisions targetting towards
+simplicity of understanding, covering most of the OS classical
+concepts, but not aiming at proposing yet another full-fledged
+competitive OS (Linux is quite good at it). However, for those who
+would like to propose some enhancements, we are open to any code
+suggestions (patches only, please). And yes, there might be bugs in
+the code, so please send us any bug report, and/or patches !
+
+The OS comes as a set of articles (in french) to be published in the
+journal "Linux Magazine France". Each month, the part of the code
+related to the current article's theme is released (see VERSION file),
+and the resulting OS can be successfully compiled and run, by booting
+it from a floppy on a real machine (tested AMD k7, Cyrix and Intel P4
+pentiums), or through an x86 emulator (bochs or qemu). The resulting
+OS is available as a multiboot compliant ELF kernel (sos.elf) and as a
+floppy image (fd.img). It provides a very very very basic demo whose
+aim is to understand how everything works, not to animate sprites on
+the screen with 5:1 dolby sound.
+
+The initial technical features and lack-of-features of the OS are:
+ - monolithic kernel, fully interruptible, non-preemptible (big kernel
+ lock), target machines = i386 PC or better
+ - compiles on any host where the gcc/binutils toolchain (target
+ i586-gnu) is available. Can be tested on real i486/pentium
+ hardware, or on any host that can run an i486/pentium PC emulator
+ (bochs or qemu)
+ - kernel loaded by grub, or by a sample bootsector (up to article 2
+ ONLY)
+ - clear separation of physical memory and virtual memory concepts,
+ even inside the kernel: no identity-mapping of the physical memory
+ inside the kernel (allows to move virtual mappings of kernel pages
+ at run-time, eg to free ISA DMA pages, and to avercome the 4G RAM
+ barrier)
+ - slab-type kernel memory allocation
+ - no swap, no reverse mapping
+ - VERY simple drivers: keyboard, x86 video memory, IDE disks
+ - logical devices: partitions, FAT filesystem, "hard-coded"
+ mountpoints only (~ MSDOS)
+ - no network stack
+ - user-level features: ELF loader (no shared libraries), processes,
+ user threads (kernel-level scheduling only), mmap API, basic VFS
+
+To understand where to look at for what, here is a brief description:
+ - Makefile: the (ONLY) makefile of the OS. Targets are basically
+ 'all' and 'clean'
+ - bootstrap/ directory: code to load the kernel. Both the stuff
+ needed for a multiboot-compliant loader (eg grub) AND a bootsector
+ are provided. The bootsector may only be used up to article 2.
+ - sos/ directory: the entry routine for the kernel (main.c), various
+ systemwide header files, a set of common useful C routines
+ ("nano-klibc"), and kernel subsystems (kernel memory management,
+ etc...)
+ - hwcore/ directory: Low-level CPU- and kernel-related routines
+ (interrupt/exception management, translation tables and segment
+ registers, ...)
+ - drivers/ directory: basic kernel drivers for various (non CPU)
+ devices (keyboard, x86 video memory, bochs 0xe9 port, ...). Used
+ mainly for debugging
+ - support/ directory: scripts and configuration files to build the
+ floppy images
+ - extra/ directory: a set of configuration files to be customized for
+ non-x86 host installations (yes, we primarily develop SOS on a ppc, for
+ the x86 target of course), or for grub-less installations. See
+ README file in this directory.
+
+The code is licensed under the terms of the GNU GPL version 2 (see
+LICENSE file).
+
+Enjoy !
+
+ David Decotigny, Thomas Petazzoni, the Kos team
+ http://sos.enix.org/
+ http://david.decotigny.free.fr/
+ http://kos.enix.org/~thomas/
+ http://kos.enix.org/
+
+
+--
+David Decotigny
+
+PS: Made with a Mac.