Review of Operating Systems

This page is under constant construction.
Please help me enrich it, by sending annotations to existing pointers, new pointers, and the usual feedback.

Please tell me about any other interesting pointer you know, that may relate somehow (anyhow) to the Tunes project...

Updated October 9, 1999 by Emmanuel Marty: Minor updates and fixes.

Contents

• OSes proper
  • Free OSes
    • Original OS Projects, that try to go beyond traditional system design.
    • Free Unix akins and alikes, that try to perpetrate, with local enhancements, the traditional OS bloat.
    • Free projects that you can join
    • Dead projects that could still be used for learning
    • Educational OSes, used in Universities to teach traditional OS design.
  • Commercial systems and their clones (free or not); they embody what is available to the common of mortal men.
    • Original contributions
    • Commercial embedded operating systems
    • Commercial Unices
    • DOS-class systems and extensions
    • Losedoze-class systems

• OS Related pointers
  • Indices about OSes and related subjects
  • Several memory management policies and their implementation in real-world OSes.
  • Some research Laboratories about operating systems.
  • Places to find Source-Code inspiration while writing a new OS for PCs.
  • PC bootstrapping and other inspiration
  • PC and compatibles hardware information
  • Generic hardware information
  • Other OS-related pages

Of course, do not forget languages that are another side of computing systems.

Free OSes

Original Free OS Projects

• 2K (formerly known as SPINE) is a distributed, reflective, component-based, adaptable operating system being built by researchers at the Systems Software Research Group from the University of Illinois at Urbana-Champaign and the Systems and Communications Group from the Universidad Carlos III - Madrid.
• Aegis (developed at MIT's Parallel and Distributed OSes group) is an OS based upon the idea of an "ExoKernel" (much like the NoKernel idea behind Tunes: there is no more runtime kernel in the OS, which yields up to 10000% performance gain). Also see D. Engler's page, and the various Exokernel and networking papers.
• Andy Tanenbaum's Amoeba, the reference among distributed OSes, is now free. To take full advantage of its distributed programming model, related programming language Orca has been codevelopped.
• The Cache kernel papers and actual implementations (in the works): Freedows and
• Choices, an OO OS in C++ (yuck).
• Jonathan S. Shapiro's EROS: Extremely Reliable OS
• Coyote from Dublin Trinity College, an object-oriented, reflective operating system supporting meta-object protocols, distribution, and runtime reconfiguration in order to meet changes in non-functional requirements (ie. dynamic customisation).
• The Flux project at university of Utah has been developing an OS toolkit (mirrored in Australia), now release 0.97, so anyone can make their own OS from bricks. It is also developing its own Fluke microkernel on top.
• The Fox project from CMU to write an OS using (an extension to) the programming language SML.
• Grasshopper, the orthogonally persistent distributed OS from Australia (mirror in UK; also here)
• HOPE at the Oregon Institute of Science and Technology, a set of primitives on top of a virtual machine, for optimistic programming, i.e. guessing the result of operations in order to increase parallelism.
• ITS (Incompatible Timesharing System) was a famous operating system written by hackers at MIT for the DEC PDP-6 and PDP-10 family during the 1960's and 70's.
• L3 and L4 by Jochen Liedtke at GMD are microkernels to demonstrate how optimizing performance requires OS kernels to be completely hardware-dependent, and even CPU-version dependent in a same family of CPUs. Due to copyright problems, authors are rewriting a clone of it under GNU GPL: Fiasco. L4/MIPS (+L4 manual).
• Jecel's Merlin project of a SELF-based OS (and here a paper about it).
• Mungi is the OS project that originally proposed a one global distributed shared memory (starting with 64-bit virtual address space).
• NOW (at Berkeley) is a operating system allowing inexpensive workstations to work in cluster, harnessing their resources to match a large computer. It uses an high-speed, high-bandwidth, switched network, in order to dispatch the load over the physical hardware.
• Off is a distributed microkernel that transparently migrates light-weight processes ("shuttles") over the network, communicating by distributed IPC ("Portals"), in a one global distributed shared memory space. By Francisco J. Ballesteros & Luis L. Fernandez at University Carlos III of Madrid. C/Web literate programming sources available. Reminds of the Mungi project...
• The Opal project, yet another distributed single (wide) address space OS with page-level protection, implemented on top of Mach on Alphas.
• Pegasus and Pegasus II from the University of Cambridge, whose purpose is to support applications requiring a constant quality of service.
• The PUMA project from New Mexico, for distributed memory architectures.
• The SCOUT project, an operating system specifically aimed at network appliances (webcams, ip routers..) from the University of Arizona.
• The Sombrero project, an operating system, providing an unique address to objects in a global address space, much like Mungi.
• SPACE from University of Santa Barbara, which implements protection as multiple layers, rather than the classic kernel-user scheme. It allows for running concurrent, different implementations of memory management or threads scheduling, for instance, as they are implemented as application code.
• SPIN OS from University of Washington, which allows applications to migrate code in kernel space, implementing new functionality or replacing default policies.
• The Sprite distributed operating system from UCB (project terminated, but still some useful information there).
• Henry Massalin's Synthesis kernel, the first of the modern OSes that dynamically generated code at runtime. Although it was written in MC68000 assembler, it opened the path to projects like Aegis and Synthetix.
• OGI's Synthetix project of fine-grained incremental partial evaluation in OS kernels, using a combination of highly isolated system components, and dynamic code generation.
• The irish Tigger project is developing a framework for the construction of a family of distributed object-support platforms.
• TUNES, the very project hosting this page, encompasses an OS project, mind you, even if it goes far beyond a mere conventional operating system.
• VINO (at Harvard) is an operating system built of reusable, replacable components that can be organized by the end-user, even code running in kernel mode. Their motto is that the kernel should provide mechanisms, not policies, and let the end-user decide of what policies to apply. A concept springing up in most new OS projects and that we can only agree with.

Free Unix akins and likes

• The BSD family used to be the reference for Unix systems. Since then, the standard has become POSIX, and 4.4BSD has split into lots of diverging projects: FreeBSD (a successor of 386BSD) is mostly for the intel platform, and is most up-to-date among BSDs regarding device drivers; NetBSD focuses on portability and networking and supports tens of platforms; OpenBSD OpenBSD has split from NetBSD, and focuses on stability and security. Lites is a BSD "singleserver" over the Mach microkernel. They all seem to have some binary compatibility with Linux, at least on the i386 platform.
  Here is a comparison of FreeBSD and NetBSD
• GNUStep (european mirror here) is a project to implement a free clone of NeXTStep (see FAQ).
• The HURD is the OS from the GNU project, also built on top of GNU Mach4 (alpha release here)
• Linux is a free POSIX.1 compliant UNIX(tm) implementation written by Linus Torvalds and lots of people on the Internet.
  • Though it was originally developed for 32 bit intel PCs, it now also runs on Alpha (64 bit!), ARM, Sparc, Ultrasparc, m68k [runs on Atari and Amiga (also here) and even PalmPilot; development underway for Mac (also here), and for NeXT Cube], PowerMac (including a version on top of the Mach microkernel mklinux) and other PowerPC (also here), MIPS (including some SGI workstations), HP-PA (with mklinux), and perhaps more (?) with lots of other ports in progress, including 16-bit i8086 (aka ELKS, download here), VAX, etc.
  • Here are some canonical Linux WWW pages: linux.org (slow), linux.org.uk (fast, but in UK), metalab.unc.edu, kernelnotes.org, redhat.com, debian.org...
  • Documentation can be found from the The Linux Documentation Project (LDP), an effort to produce a series of books/articles/manuals to document Linux. (the LDP page also has many links to other Linux related sites). Linux Manual pages WWW access can be found here.
  • For us Kernel Hackers, here is the online Kernel Hacker's Guide
  • If you seek help on Linux, you should first check all the documentation above. Also, individual packages have READMEs, FAQs, and local documentation that you should check (sometimes only available in the source distribution, not in binary packages).
    If you still don't succeed after carefully reading the docs many times, you might ask for help on one of the IRC networks: OpenProjects (channel #Linpeople), Undernet (channel #Linux), EFnet (channel #Linux), DALnet (channel #Linux), etc.
  • If you want to toy with both Linux and Open/Net/FreeBSD, a lot of useful information is available in the Linux+FreeBSD mini-HOWTO.
  • Finally, people who want to develop a graphics system on their OS should definitely have a look at the Linux project and standard to be, GGI (the Generic Graphic Interface).
  • Linux is not just a fun OS. it has lots applications in the so-called Real-World, such as Linux Equipped Astronauts, rendering for the movie Titanic, or running mission-critical servers. Not even mentioning running a growing number of internet servers, and just as much in large companies such as Apple or Novell.
• Mach is a free microkernel upon which many experimental OSes are built; There exists "ports" of classical unices to Mach, BSD (Lites) and Linux (MkLinux), consistently slower than their "monolithic" counterparts.
  • The original CMU Mach project is now ended with Mach3 (see Published and Unpublished Mach Papers). Some pretty interesting ones are available here. Two different groups are working on two divergent further versions of it:
  • The Open Software Foundation is officially developing its version of (free) Mach, MK4, for use by its members' (commercial) OSes.
  • Mach4 is now developed by GNU as the continued basis for the HURD, its free microkernel-based OS.
  • The Flexmach project itself tries to implement objects above Mach in C++ (yuck) according to the related OMOS model and implementation over plain unix. (people at University of Utah have stopped maintaining Mach4, as their terminated Flexmach, and concentrate on their new Flux project and Fluke microkernel)
• THix is a deceased project of an unix implementation written from scratch for the purpose of learning. The project hasn't been touched since 1996 but it boasts impressive functionality for a system developed by a single person.
• Andy Valencia's VSTa fine QNX- and Plan9- inspired but free open-developed microkernel-based OS; its mailing list archive and its distribution.

Free OS projects in early stages of development

• Alliance OS is a split from Freedows below. Its goal is to implement a system based on isolated components, described with the Corba IDL and communicating through a System ORB. This project is currently very organized (I'd say, lots of bureaucracy) but documentation and code are still sparse. Updated july 2nd with some more code; most subteam websites are still empty though.
• J. Spencer Seidel's Apostle Operating System project, initiated early october 1999. This is a project for a new, free operating system, but at this point they are still gathering people and organizing themselves, so there is not much technical information available, besides a small test kernel. Keep an eye on it though.
• Alaric B. William's ARGON (has got a mailing list) are set out to write an operating system which dynamically compiles high-level languages to machine code as needed, and where all parts (ARGOT modules) are orthogonally persistant, and communicate through a network-transparent messaging protocol based on globally unique addresses, whether local to the system or on the other side of the world.
• The Amiga Research OS project, lead by Aaron Digulla is rewriting a free software clone of AmigaOS from scratch (however, current licensing status unclear -- beware!), hoping to fix bugs and legal problems with the original OS, and finally port it away from the deceased (until further notice) Amiga hardware platform to the i386 PC and other platforms (PPC, Alpha, whatever).
• Brand Huntsman's BRiX OS will be based on modular functions that can be dynamically called by other functions. The microkernel is being developed in assembler but the functions will be written in a language native to BRiX. Its persistent object store, automatically downloadable functions, and a new user interface will make it very easy to use for both beginners and experts. From what I understand, every function runs in a seperate thread. No sourcecode or useful binary image have been released so far, though. Brand can be seen at times on the OPN IRC network, channel #tunes.
• ChaOS, like OpenBLT below, is a cleanroom implementation of an operating system based on a microkernel (codenamed Storm), announced over the summer; there is both code and documentation available on the site, as well as a downloadable and bootable demo floppy that will let you try your hand at it in no time. Like OpenBLT, the code seems pretty clean and nice so far, and news/code updates are done regularily. Definitely a project to follow.
• Samuel A. Falvo II's Dolphin is an operating system for PC and compatibles; the project has been going for some time and has undergone several conceptual changes. Samuel has adopted a virtual machine scheme, where only a VM runs in ring 0 and all the rest of the system is implemented as ring 3 shared libraries (much like AmigaOS). These libraries use VM calls in order to access the underlying hardware. There is actual code floating around for this project, such as a bootsector that you can tune to boot your own protected mode OS. There seems to be actual progress this summer. Check all of that out from their homepage.
• Daniel Vila's EROS (unrelated to the extremely reliable OS), a microkernel written in C++ and x86 assembler, and its Fenix subsystem currently in planning stage.
• Reece Sellin's Freedows Project for an OS that would be binary-compatible with multiple existing OSes including Windows. Based on the stanford "cache kernel" principle, it aims at providing application kernels that in turn provide functionality of Windows, Linux, MacOS or other systems, to unsuspecting applications written for these systems, all at the same time. Most developers however split to implement these goals in the Alliance OS project. The site has undergone a complete redesign, and we're announced in veiled words that the entire team has been replaced and the system is being redesigned. No actual code at this point, but the project is still alive.
• Fabricio Rocha's Geex! operating system, where the philosophy is to make an OS with a very small footprint, working on old computers, and completely free. The project is still in the process of starting, and no code has been written yet. However, the site has a lot of interesting documentation on OSes in general. Documentation on Geex! itself is still sparse and sketchy, but there are beginnings of several proposals.
• The JOS project wants to create a free, open operating system based on the Java(tm) technology, ie. a free clone of JavaOS(tm). They have a mailing list you can subscribe to. The project looks like it's starting to take off. Follow closely !
• Redhog's KangaroOS, an operating system implementing multitasking by providing a virtual machine to each process; processes can also have subprocesses that they can schedule at their liking. There is a lot of documentation and some sourcecode available, currently completely in assembler, and building under DOS (scroll down the left frame to get to the OS pages proper).
• Knewcleus is a microkernel-based OS that aims for POSIX compliance; while open sourced, the people behind it intend to make it a commercial venture and release a packaged version that will include additional things not present in the opensource version. There is documentation on the site and code can be downloaded via CVS. Work has just started on adding real-time capabilities to the system.
• KOS is a small project of developing an operating system being worked on by a few French people. Like LittleOS, it seems to be a nice little project to work on if you're interested in operating systems and want to hit the metal, but don't know where to start. Progress seems to be very slow this summer; hope it picks up speed again in the fall. Note that the site has some pretty interesting OS documentation as well.
• LispOS has just appeared as a project to revive the still unequalled systems that ran on Lisp Machines of the past, this time making it free and running on standard/cheap hardware, instead of proprietary and requiring non-standard/expensive hardware. Relevant pages at cathcart.sysc.pdx.edu, [MIA] neosoft.com, and Joe Marshall's former www.eval-apply.com
  Those interested in the discussions may read the archives of the mailing-lists, or subscribe to them (no more). lispos, and lispvm.
• LittleOS is a small operating system experiment being developed by a group of individuals. It hadn't been updated in some time and was thought to be dead, but a 0.3.0 release came out recently. It has no big pretentions whatsoever and is just meant to experiment with OS techniques and programming in group.
• Julian R. Hall's Moscow is about implementing an operating system as libraries of reusable and replacable objects. Julian is currently developing tools that will later help him realize his goal (such as his NetWide assembler (nasm), so no OS code has been written yet, although design documents have been updated.
• Nitros-9 is basically a reconstruction of OS-9 for the 6809 Tandy CoCo3, but refined for the Hitachi 6309 compatible CPU. Development group is pretty small, 'cause the hardware is pretty rare these days, but it is a fascinatingly loyal bunch of dedicated OS hackers.
• Brice Rey's's NTDIOS is a working 32-bit, multitasking, operating system for x86-based computers, running in protected mode. Progress is constant, there is a bunch of code and a lot of documentation available. However, note that the entire site is in French :) as are all developers.
• Brian J. Swetland's OpenBLT cleanroom implementation of a microkernel. Conventional implementation of processes and threads, but the codebase was written from scratch and works to some extent. A nice project to join if you want to help build an OS that already went beyond the bootloader stage. The system is updated on a regular basis, seems to have gathered a few more developers and development seems nicely organised.
• "Joker" Josh MacDonald's OSDEV
• OS-DeViLs project (with an hardware independence page here), is a federation of people hacking new OSes, so they can debate ideas, exchange experiences, and share code.
• Balazs Miklos's Phantom OS is a project for an operating system for x86 PCs, based on a microkernel, and released under the GNU General Public License. Currently the kernel is being developed, but the plan is to make a full OS around it as time passes. There is sparse documentation but also some actual code to download.
• Prool's Proolix is yet another Unix clone project for the old 8086 PCs, from former USSR.
• Raven (a new page soon to appear here) is another attempt at making an OS for x86 PCs from scratch. The project is still in the bootblock phase and documentation is still at wish-list stage, so I can't report much on the design goals of the OS; but the more systems around, the better.
• Tom Novelli's retro is actually a prototype low-level infrastructure for TUNES, written in x86 NASMbly, and growing a FORTH environment.
• Frank Barrus' ShagOS is a (running) OO system based on a message passing kernel. The OS itself hasn't received work in a while, however, this site is still regularily updated, and it features several very nice tools, such as SOLO (a very advanced bootloader, that includes debugging, environment vars and filesystem support, and reminds me of Sun computer PROMs), and DECO (a "dynamic" C++ to C++ compiler).
• Brian Klock's ShawnOS is a small system, written in 3 months entirely in assembler, that is functional enough to run programs. It was written originally as a college exercise but the author kept working on it.
• SkyOS is yet another new operating system for x86 PCs. Its design is pretty standard; monolithic kernel and growing with a mushroom-like development, features and code being added as needed without much planning. However, it boasts impressive functionality (IMHO) for a project written from scratch: not only it runs programs, features a GUI and all common drivers for pc hardware, but as well a TCP/IP stack and other goodies. Even if there isn't much thought put into design, the amount of work done deserves respect. A nice project to join if you want to work with a large base of already working code and a functional system.
• SwarmOS is a pretty standard, kernel based OS, but that actually boots and works to some extent. There isn't much documentation available on the site (besides a message board) but all sourcecode can be downloaded, and there are docs in the archive.
• Michael Gerhards' UniqueOS plans to make an OS based on no fixed data structures, using a technique called tag items, borrowed from AmigaOS. More information and documentation can be found on the site. A few sources can be downloaded.
• Jascha Wetzel's XOS aims at being an object-oriented, distributed, preemptively multitasked/threaded, message-passing based system. While this would sound like pretty standard marketroid talk, the site contains very interesting, detailed and clear documentation about what the author has in mind, an object-oriented microkernel where every part of the system does one thing and does it well, without any of the other parts knowing the details; a definite plus for scalability and future expansion. The author also cares to define the concepts he uses, so have a look at it even if you don't do C++ in your sleep. The actual implementation hasn't started yet, but definitely a spot to watch.

Apparently dead OS projects

• Kinfira's Antares OS for x86 PCs, that seems pretty much dependent on x86. Intended to become a microkernel type of design; left dead at function loader and draft filesystem stage.
• EOS (ask Cleo Saulnier) was an operating system specially designed to run games under. The project looks like it has been abandoned. If you're interested in such a project, probably the best would be to mail Cleo and see if you can profit from what has already been done.
• JeniOS is a project that started recently and then didn't give any updates. It aimed to develop an operating system with a radically new interface (a la Kai Power Tools) on top of the CMU's Mach microkernel. They seemed to believe that Windows NT is based on Mach as well though... Strange.
• LOS was meant to be another OS for gamers, like EOS. However, this one booted and worked, and there were a few games for it (like an arkanoid clone).
• Frank Kudermann's O/OS introduces a new GUI concept, and aims at architecturing the operating system around reusable, replacable components. Work on the system seems to have stopped, though.
• Joel Utting's Platform OS wanted to achieve platform-independence through a low-level virtual machine. The project seems to have died during planning and specification stage.
• Bart Sekura's TINOS aimed at making a small, multipurpose OS that could be used as a learning tool for the author and anyone else that cared to use it. However it has been last updated in march of 1998.

Educational OSes

• Minix is Andy Tanenbaum's famous unix-like OS for x86, m68K and sparc.
• NachOS from Berkeley, demonstrates the principles of the traditional unix-like model.
• Topsy by George Fankhauser is a microkernel, ported to the R3000 architectures (for which emulators exist).

Popular Commercial OSes and their clones

Original contributions from Commercial systems

• AmigaOS
• Sony CSL's Aperios (formerly Apertos), a Reflective OO OS
• Be's BeOS.
• GEOS (originally developped by Geoworks, now taken over by New Deal) is some very fine OO OS for various kinds of computers (including PCs), that comes with a GUI and various office applications. One of its most notable aspects is that it isn't a resource pig: it already provided a GUI to 8-bit computers (C64, C128, Apple ][), and multitasks fine even on 8088 computers (but takes advantage of intel 32-bit mode when available). It has consequently been ported successfully to various hand-held platforms.
• MacOS X server, the next version of Apple's highly proprietary system, will not be based on the Copland development project, nor on a cross with NeXTStep called Rhapsody, but is designed as the friendly MacOS graphical layer over 4.4BSD on top of the Mach microkernel. It will apparently feature a way of running current MacOS software.
  Here is a good page about finding real OS software for MacIntoshes.
  Conversely, ARDI is selling a MacOS emulator for PCs (more or less System 6/7 compatible): Executor. You can also find a good, free one for BeOS and LinuxPPC called SheepShaver.
• Milan the operating system. So this is what happened to the Atari ST and its TOS; bought by Milan computer GmbH, who produced new versions of the TOS: version 4.5, and a new, multitasking Milan MultiOS 1.2.
• Multics (also a mirror in UK) is the "great" OS (written in PL/1) whose design began in the late 60's, that meant to become the be-all-end-all of OS technology by having just every (un)imaginable feature, and that was supplanted by Unix, despite the fact that Multics was much better (?) designed, because Unix' simple and stubborn design was much more adapted to the very resource-poor architectures of the time.
• Apple's Newton OS was interesting. However, Apple not only discontinued production but also removed all links and documentation. Former customers and developers will appreciate. Dylan programmers will be rung a bell.
• RISC-OS (see newsgroups comp.sys.acorn.*), (a french mailing list here -- subscribe to here), is the nifty OS that runs on Acorn's ARM-based RISC PC. Remember how they were the first to introduce inexpensive RISC technology into consumer electronics to compete with the usual bloated designs? See also their Thumb technology.
• Tao OS (now called Elate) is the only OS that currently can distribute code on heterogeneous underlying networks (here their internet contact, and an old introduction to Tao OS). Was renamed Tao OS from TAOS because of legal problems.
• The Taligent company is the result of some counter-nature cross between Apple and IBM ;-) it worked on a brand new operating system, the CommonPoint application system, that attempted to change the basic programming paradigm, and which has been released on top of AIX in summer '95. To know more about it, you can browse the first two chapters of the book Inside Taligent Technology by Sean Cotter. All in all, it looks like yet another failure due to C++ introducing unmanageable complexity throughout the system.

Operating system for embedded devices

• eCos from Cygnus Solutions, an operating system runtime compatible with the japanese norm µITron, with complete source code available, and FREE.
• Many other free software embedded systems are also available at Cygnus' ftp site or on their sourcecode page.

• Chorus is a proprietary microkernel rival of Mach, and a RTOS (now acquired by Sun Microsystems) for telecommunication devices (cellphones, etc.) and network appliances (webphones, set top boxes..). See some slides about it, and a FAQ) is available here. There also are tech reports here.
• Nexus' coniX small romable embedded operating system for ARM processors.
• Caldera Thin Clients' DR-DOS (OpenDOS) is now being sold as a solution for embedded systems. Indeed, with a full-featured web browser fitting in 4 MB of memory, this is less of a bloat than WinCE.
• Sun's JavaOS (with a more technical page at JavaSoft) is a standalone virtual machine not running on top of any other OS; mainly targetted at embedded systems.
• Microware's OS-9 real-time OS, widely used, and still in good shape after so many years.
• QNX is a an effective, scalable, POSIX emulation capable, message passing, micro-kernel based, real-time, distributable, OS that has proven successful in this embedded market and/or on x86 systems. See their QNX papers.
• Not surprisingly, Michael Podanoffsky's RxDOS is also being marketed as a solution for embedded systems now.
• Wind River's VxWorks real-time operating system, micro-kernel based, POSIX and ANSI C compliant.
• Microsoft's attempts at fitting a large unstable desktop-PC operating system, with a hammer, into the stringent requirements of embedded systems are here: Windows CE and their latest monster, Windows NT Embedded 4.0.

Commercial Unices and beyond

• Inferno is a networked OS from Bell labs and its limbo language, successor of Plan9, the system that reinvented scoping for coarse-grained objects (my, after they ignored it for 25 years, which resulted in the whole world having systems deprived of it, the guys from Bell-labs rediscover it. All praise Hell-lahs!)
  • newsgroups about these: comp.os.inferno and comp.lang.limbo
  • Inferno News and Comment (been reported to me as very complete)
  • Some comments on Inferno
  • A presentation.
• MachTen is a commercial version of BSD4.4 using Mach on 680x0 and PPC MacIntoshes.
  There are free alternatives to it, like MacBSD.
• Plan9 OS, or what Unix should have been (by AT&T from where Unix came). It's a commercial OS, but freely available for academic use. See its FAQ. It got everything right as for proposing a uniform system interface (the dynamic, per-process name->channel "filesystem" thing) but is still wrong by using a low-level programming language with coarse-grained system abstractions. (another page here)
  See its successor, Inferno.
• Solaris-MC: Sun is working in making a distributed OS out of Unix.
• Sun's Spring System (hmm, dead link at the moment).

DOS-class systems and extensions

• A well-known company in Seattle has produced and mismaintained the most crappy OS ever, known as DOS. The dreaded name need not be mentioned here.
• The FreeDOS project for a free DOS clone, based on Pat Villani's DOS-C kernel. It currently works, though not compatible with all known DOS extensions and undocumented features (that some apps require), but they are getting there. The project is currently under very active development.
• Of course, there exist lots of DOS emulators for lots of non-DOS systems.
  For instance, Linux has quite a good free DOS emulator running on i386 architectures (also runs under *BSD). But it is actually a hardware emulator, and requires that you use an actual DOS software (e.g. OpenDOS or FreeDOS) to run on top of the virtualized hardware. Newer versions of DOSEMU will be released as a bundle with FreeDOS.
• Caldera has released DR-DOS 7.03 an free-for-non-commercial-use version of DOS (was once released as OpenDOS, but Caldera reverted to the historical name). It's basically the very stable and complete implementation of DOS by Digital Research, with some networking and multitasking capability, ROMability, etc.
  Sources for the kernel have been released, but the free software community that gathered around that event (FAQ here and there) felt betrayed because Caldera did not make the system free of rights, and did not release all the sources after all. Go FreeDOS instead!
  Caldera also sue the above-mentionned Seattle-based company for unfair competition practice in forcing people and vendors not to buy from competitors, at the time DR-DOS was technologically way ahead.
• IBM's OS/2 is an OS that's halfway between DOS and Unix (some say the best of both world, others say the worst). It can emulate most DOS programs seamlessly, has a nice GUI (users say), but was never marketed well, and is now abandoned by even IBM! Good development information is available on the Team OS/2 and Seattle OS/2 users group site.
  FTP sites for OS/2 software: Hobbes, FTP-OS/2
• Other commercial DOS clones include:
  • PTS-DOS is a (commercial) DOS clone from Russia (fast mirror in USA).
  • Mike Podanovsky's RxDOS is a (commercial) DOS clone as described and available in the author's book "Dissecting DOS".
  • TSX-32 is a 32-bit (commercial) OS for PCs with small memory requirements that can also emulate DOS (and run Windows ?).
  • I've also been told about SuperDOS, ROM-DOS, Real32, Multiuser DOS.

Losedoze-class systems

• The The Cygnus GNU-Win32 library allows you to simulate a GNU system on top of Win32, thanks to the cygwin32.dll
• Here are links to the unnamed horrors: *NT Workstation and *NT Server; *95.
• WINE free WINdows Emulator for Unices (also here).
• Jason Filby's ReactOS project, aiming to produce a free Windows NT 4.0 clone distributed under the GPL license. The developers of the project keep a low profile, however they are making big strides. ReactOS is now able to boot and start simple win32 console-based applications. Best luck to them for the rest of the immense work.
• Note that there also exist commercial clones, among which the Sun WABI that runs 16-bit Windows apps (soon 32-bit apps too, they say) on your X/Unix workstation. Also exists for Linux, as commercialized by Caldera.

OS Related Pointers

• Indices about OSes and related subjects:
  • The FAQ from the comp.os.research newsgroup; also its archive; it is a good FAQ, and anyone interested in OS implementation should have read it.
  • 500mhz.net's operating systems index, sorted by date of discovery (not updated in a while).
  • Brad Appleton's links to operating systems news sites and development resources.
  • Sven Paas' comprehensive german page (in English). Now moving here ?
  • Patrick Bridges' arizonian page
  • Christopher Browne's Novel OS work, featuring a detailed description of several operating system projects.
  • Vinny Cahill's [MIA] irish page
  • Hyogun Lee's own OS page.
  • Kang Sung's OS page in korea.
  • OGI's oregonian page
  • Nemo's OSes links
  • Embedded and Real-Time OSes.
  • Patrick Gunn's OS page and webring.
  • Seoul national university OS labs operating systems links
  • SIGOPS Create your own OS tutorial, describing the basic steps involved in writing an operating system, if you don't know where to start.
  • Yahoo's page about Operating Systems
  • Gustavo Zamboni's computer architectures and OSs on the web, a very comprehensive list of links, sorted by the platform they relate to. No description is made of what you will find in any of them (besides the site name), but the list is very large and interesting.
  • AltOS, "practical alternatives to microsoft operating systems". A guide of all 'alternative' systems like MacOS, Linux, BeOS, with screenshots and descriptions.
  • OS/A65 is an insane (and functional project): a multitasking operating system for old CBM computers like the C64, with TCP/IP and all. Not useful for much, but still worth mentioning.
  • OS doc at ftp.funet.fi
  • Distributed Algorithms & Systems
  • Process Migration & Load Balancing
  • Checkpointing

• Here is some information on memory management issues and common policies:
  • People working on Garbage Collection have a LOT to teach us on memory management.
  • A Virtual memory tutorial, describing the motivations behind that common technique in modern OS'es, its theory and potential problems, and actual implementation issues.
  • Proposal for a Zone allocator for Linux, and the homepage for Linux memory management, by Rik Van Riel. Quite informative about how kernel memory allocation works in an OS used for real-life applications outside of the testing lab, some problems with its current scheme and potential solutions.
  • Dynamic memory allocation implementation in userspace under Linux/ glibc. Different policies than what the kernel does.
  • The BGET memory allocator; another set of policies for userspace memory management and their implementation.
  • FreeBSD's newvm, the new memory manager for that free BSD/Unix clone. Another design and implementation for a real-world system, worth a look for anyone developing a memory manager for their OS.

• Here are some research laboratories interested in operating systems (send me more addresses):
  • Xerox PARC
  • Sony's Computer Science Laboratory
  • University of Washington CSE department
  • Oregon Graduate Institute CSE research topics and groups
  • Sun Microsystems Inc. laboratories (ex-SMI Technology and Research).
  • The Open Group Research Institute and their OS group in Grenoble, France.
  • The IEEE Computer Society's TCOS (Technical Commitee on Operating Systems)

• Here is some code that you can link into your OS and relieve you from the hassles of blindly getting it to boot, by providing you boot software and basic I/O:
  • Etherboot and its successor NILO allow x86 PCs to boot an operating system across the network; they include code and tools for producing EPROMS that can be placed on the corresponding network card sockets so that diskless PCs can download and start an operating system kernel, using standard protocols (bootp, dhcp, tftp). They can boot systems like Linux this way, but are easily adaptable to your own.
  • The Flux project's OS toolkit.
    The Flux OS kit is a complete modular infrastructure that provides all the bricks needed to easily build an OS, focusing on what interests you, and reusing components for the rest. Newbies have reportedly transformed Unix programs into standalone OSes in a matter of hours, using it.
  • GRUB the grand unified boot loader for PC and compatibles. Originally written by Erich Boleyn, it has been taken over by the GNU project, as Erich didn't have any more time for it, but GNU depend on it for the HURD. The original (with documentation, and also specification of the multiboot standard) could be found here; the new GNU GRUB is here with even more impressive functionality.
    As mentioned, GRUB is used by the HURD, and it can also boot *BSD, Linux, DOS, and more. It's got facilities for accessing the filesystem at boot time, so you can safely write your loader as just another 32-bit process.
  • Dolphin bootsector is a bootsector primarily designed to boot Dolphin, as the name says, but the author is nice enough to have written documentation about how to boot your own OS project from it; it handles all protected mode and paging setup for you; the whole thing fits in 1 KB so it could be useful when you don't have much room, like on a floppy.
  • SOLO the ShagOS boot loader, includes useful x86 debugging features.
    SOLO not only includes boot-time filesystem access, but extended IO and debugging facilities; might be great to hack your kernel. Its license is now unrestricted, so that you can now freely use it and distribute it with your code. SOLO is definitely worth a look.

• Here are some sources of inspiration for people developping a 32-bit OS on PC's:
  • DOS extenders in the x2ftp archive (some interesting docs around, too, particularly the PCGPE)
  • Free Embedded systems from Cygnus FTP
  • Some 32-bit FORTH systems from the taygeta archive
  • The Guide to x86 bootstrapping describes the operations performed by a PC compatible computer BIOS at boot time. Useful for writing OS boot loaders, boot managers and such.
  • David Lindauer's software
  • FAQ about how to create bootable CD's for PC in the "El torito" format. Useful when you'll have written an OS large enough to fill a CD..
  • os-dev page for the intel architecture
  • 500mhz.net operating system development resources
  • The Linux Assembly-HOWTO about better (more portable, maintainable, seamlessly integrated) ways to include assembly code in your projects (shameless plug for Fare).
  • Gareth Owen's Gaztek site, which contains a lot of information on OS development and programming the PC hardware, as well as a gimmick OS (GazOS) and even a small webserver (ghttpd).
  • and of course, the code for all the free OSes above, including Tunes.

• PC hardware information
  Efficiency-aware OS implementors must have some idea of how the underlying hardware behaves.
  The cheapest bang/buck for a complete system currently is available through old or new PC-compatible computers.
  • OS programmers might be interested to get the CPU specs directly from the chip builders: Pentium, Pentium II, and Pentium III manuals, as well as other documentation from Intel, Cyrix, and AMD.
  • Unofficial CPU information Very extensive information (including undocumented features) on the x86 family of processors is available at Robert Collins' famous x86 site and Christian Ludloff's sandpile.
  • A great source of information, and a useful tool for building and testing x86-based OSes is Bochs that fully emulates in software the 386+ PC hardware, on any 32-bit+ machine. Able to boot Linux, FreeBSD, Win95, Roadrunner and many other operating systems.
  • Hardware and low-level programming information on common PC motherboard components is available from Craig Peacock's Interfacing the PC series : parallel port ( standard, enhanced), serial UARTs, keyboard, and the Programmable Interrupt Controller.
  • There is an impressive amount of documentation on PC architecture and associated peripherals (NICs, ATAPI/IDE, VGA, mouse, Flash memory.. and also higher level like all network RFCs) at the Ronis site. A definite good starting point if you need documentation for writing your own system.
  • PC demo coders have also gathered information about the underlying hardware, for instance on cdrom.com's demo coding hardware pages, or Cubic's very extensive hardware archive.
  
  
• Other hardware
  • Another widely used (albeit nowhere as much as x86) is the PowerPC. Motorola provides programming documentation in Adobe PDF format on their tech support site., as well as documentation of their new MMX-alike AltiVec technology. You can find some more programming info (also in PDF) at this place.
  • The CPU Info Center covers all mainstream CPUs in the current competition.
  • But MISC technology is not mainstream yet, though very promising, and already the best computation-horse-power/electric-power-consumption ratio. See Jeff Fox's page, the MISC mailing list (now at Elijah labs) or iTV's page. (the SISC312 seems around the same design, too). If you're interested in CPU design, Jeff Fox sells a DYOP (Do Your Own Processor) kit based on FPGA...
  • The Chip Directory talks about chips in general, CPU included, but not exclusively
  • For a historical point of view, check this page about Great Microprocessors of the Past and Present

• Other OS-related pages
  • The Tunes Review page on Virtual Machines
  • Loughborough University high-performance networking and distributed systems archive
  • An Operating System Vade Mecum by Raphael Finkel
  • Dynamic recompilation resources: good introductory papers and concrete applications on dynamic code generation (ie. in reflective sytems) and recompilation (ie. in emulators that need to dynamically translate emulated code to native opcodes, for speed).
  • About UNIX:
    • UNIX Reference Desk
    • An overview of the POSIX standard.
    • A nice article about UNIX literacy
    • Unix Haters is a collection of jokes and arguments against Unix. This page does not tackle real problems, is often unfair, and not even funny. If the book reads the same, don't buy it (now, if someone actually reads it, I'd welcome a real review).
  • How reliable is your OS? How good is its support? How fast are dangerous bugs fixed? Check the ping o' death page to see...
  • How to write a systems paper (get a text version by sending body "send advice papers" to info@usenix.org)

More netsurfing

• The TUNES project that hosts this page may interest you,
• as well as its Review subproject.

To Do on this page

• Write reviews of these OSes where missing.
• Talk about the open development model, as used in Linux.
• Send a note to all the OS pages that do not cite us.
• Differentiate full OSes from OS-less kernels, putting two entries when the kernel could be used without the OS, even though only one OS currently exists over it.
• Still have to add these...
  • Server OS Technical Comparison
  • GLOBE as well as to all pages pointed in various OS indexes...
  • bibliographic pointers from the OS FAQ: cstr, German Bib, Arizonian Bib, bibliographies, UFS 93.
  • refdbms
  • Find out more about STAPLE, a persistent lazy-functional-language based project (FTP).
  • FTP sites with OS-related stuff: in France, England, Taiwan.
  • FTP pointers from the OS FAQ: Clouds, Cronus, Guide, Horus, Isis (also here), X kernel.
  • Rumor, a user-level version of Ficus, an optimistically replicated file system (see a summary of Ficus and a description of Rumor). Unfortunately, Rumor is not yet being distributed.
  • Books:
    • "OS Concepts and design" by Milan Milenkovic
  • at AT&T, Mr Douglis' CCache paper (?)
  • Brian Bershad or Calton Pu
  • Doug Jensen: dynamic real-time distributed computer systems
  • Neutrino: POSIX in 64K (see QNX)
  • oslr2 is an idea of an OS much like IBM's VM/CMS: provide people with a low-level virtual hardware abstraction facility that multitasks by spawning itself.
  • Aditya Bansod's OSS and OSS2 are operating system simulators for Windows that implement their own OS ontop, and provide abstraction for local processes.
  • Dave Hudson's Artemis, and now, Constellation
  • Nicklaus Wirth's Oberon is not only a language, but also an OS...
  • DVM
  • Alto
  • Trusted Information Systems offers information on Trusted Mach, a B3 certified Mach, and Triad, an experimental distributed, real-time, trusted operating system based on Trusted Mach.
  • The Open Group is concerned with security in the context of its DCE
  • the MK++ kernel Another project aiming at Mach compatibility and security is DTOS
  • application of formal methods towards the MK++ microkernel.
  • Distributed Trusted OS
  • RTOS form
  • RCOS.java
  • fide-95-121
  • theos software
  • OS Sucks-Rules-O-Meter
  • Grail
  • EssenceOS

Back to the Review subproject.