Educational OSes

These are instructional OSes developed and used in some Universities for their OS courses. They are freely available, and have some docs, too. In portable C, unless stated otherwise.

• 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).
• Xinu, a widely respected "vehicle for teaching Operating System design concepts". It supports most modern OS functionality, including message passing, tcp/ip, and an independent shell.

Elephant: The File System that Never Forgets

Douglas J. Santry, Michael J. Feeley and Norman C. Hutchinson
University of British Columbia

Alistair C. Veitch
Hewlett Packard Laboratories

"Modern file systems associate the deletion of a file with the release of the storage associated with that file, and file writes with the irrevocable change of file contents. We propose that this model of file system behavior is a relic of the past, when disk storage was a scarce resource. We believe that the correct model should ensure that all user actions are revocable. Deleting a file should change only the name space and file writes should overwrite no old data. The file system, not the user, should control storage allocation using a combination of user specified policies and information gleaned from file-edit histories to determine which old versions of a file to retain and for how long.

This paper presents the Elephant file system, which provides users with a new contract: Elephant will automatically retain all important versions of the users files. Users name previous file versions by combining a traditional pathname with a time when the desired version of a file or directory existed. Elephant manages storage at the granularity of a file or groups of files using user-specified retention policies. This approach contrasts with checkpointing file systems such as Plan-9, AFS, and WAFL, that periodically generate efficient checkpoints of entire file systems and thus restrict retention to be guided by a single policy for all files within that file system. We also report on the Elephant prototype, which is implemented as a new Virtual File System in the FreeBSD kernel."

The Elysium Project
http://elysium.sourceforge.net/ 

Although recent research has shown that it's possible to build generic operating systems that allow an application - such as a web-server - to gain an eight-fold increase in through-put traditional operating systems, such as Linux, are still considered adequate. How come? 

The Elysium Project is a radical new operating system design. By exterminating all abstractions from the operating system itself it allows for higher levels of application control with increased flexibility and performance as results. 

We're currently seeking designers and developers for the Elysium Project. If you want to participate in the design and implementation of the software, become a beta tester, manage the Elysium web-site, or just have a look at the current source code, please visit our web-site. Date: 02/04/00 12:26  

Embedded OS 
 OS in handhelds, home appliances, cars a.s.f. 
  MS-Windows-CE 
  Java 
  Epoch32 
eCos 

Emulator

simulates an OS or a whole computer

EOS  (outdated)
EOS, german OS CP/M-compatible.
 

Epoch32 
Nokia etc preferred Epoch32 despite WinCE for their handies. 

EROS (University of Pennsylvania) Group Members
EROS (Extremely Reliable Operating System) is a new operating system being implemented at the University of Pennsylvania. The system merges some very old ideas in operating systems with some newer ideas about scheduling and performance. The result is a small, secure, high-performance operating system that provides transparent orthogonal persistence coupled with microkernel-style critical paths, including a high performance IPC subsystem.

Eumel (Extendable Multi User Microprocessor Elan System)  (outdated)
Developped by GMD and 'Hochschulrechenzentrum Bielefeld'. Eumel was a multi-user OS primarily for the language ELAN (Elementary Language). 

ExOS 
MIT Exokernel Operating System 
An operating system is interposed between applications and the physical hardware. Therefore, its structure has a dramatic impact on the performance and the scope of applications that can be built on it. Since its inception, the field of operating systems has been attempting to identify an appropriate structure: previous attempts include the familiar monolithic and micro-kernel operating systems as well as more exotic language-based and virtual machine operating systems. Exokernels dramatically depart from this previous work. An exokernel eliminates the notion that an operating system should provide abstractions on which applications are built. Instead, it concentrates solely on securely multiplexing the raw hardware: from basic hardware primitives, application-level libraries and servers can directly implement traditional operating system abstractions, specialized for appropriateness and speed. 
developed by the Parallel and Distributed Operating Systems group at the MIT Lab for Computer Science. 
 

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