Not Another Completely Heuristic Operating System

Nachos
Developer	University of California, Berkeley ; (Thomas Anderson, Wayne A. Christopher, Steven J. Procter)
Written in	C++
Working state	Discontinued
Initial release	1992;32 years ago
Latest release	3.4
Latest preview	4.0 / 1996;28 years ago
Platforms	MIPS architecture
Kernel type	Monolithic
License	Berkeley Software Distribution
Official website	www.cs.washington.edu/homes/tom/nachos/

Last updated August 02, 2024

Not Another Completely Heuristic Operating System, or Nachos, is instructional software for teaching undergraduate, and potentially graduate level operating systems courses. It was developed at the University of California, Berkeley, designed by Thomas Anderson, and is used by numerous schools around the world.

which are there to run the Nachos^[1] user space applications. That means that you can write programs for Nachos, compile them with a real compiler (an old gcc compiler^[2] that produces code for MIPS) and run them. The Nachos kernel instead is compiled to the platform of the Host OS and thus runs natively on the Host OS' CPU.

Nachos version 3.4 has been the stable, commonly used version of Nachos for many years. Nachos version 4.0 has existed as a beta since approximately 1996.

Implementation

Nachos has various modules implementing the functionality of a basic operating system. The wrapper functions for various system calls of the OS kernel are generally implemented in a manner similar to that of the UNIX system calls .^[3] Various parts of the OS are instantiated as objects using the native code. For example, a class Machineis used as the master class of the simulated machine.^[4] It contains various objects, such as FileSystem, Processor, Timer, etc. which are defined to simulate various hardware aspects.

Major components

NachOS Machine - Nachos simulates a machine that roughly approximates the MIPS architecture. The machine has registers, memory and a CPU. The Nachos/MIPS machine is implemented by the Machine object, an instance of which is created when Nachos starts up. It contains methods like Run, ReadRegister, WriteRegister, etc. It also defines an interrupt object to handle interrupts. Timer and statistics are also implemented in this.

NachOS Threads - In NachOS a thread class is defined. A thread has an associated state with it which may be ready, running, blocked or just created. The thread object has various methods like PutThreadToSleep, YieldCPU, ThreadFork, ThreadStackAllocate, etc. Each thread runs at a virtual address space.

NachOS UserPrograms - Nachos runs user programs in their own private address space. Nachos can run any MIPS binary, assuming that it restricts itself to only making system calls that Nachos understands. In Unix, "a.out" files are stored in "coff" format. Nachos requires that executables be in the simpler "Noff" format. To convert binaries of one format to the other, use the coff2noff program.

^[5]

Successors

As Nachos has not been in active development for a number of years, and possesses a number of recognized flaws (particularly with regards to portability: Nachos relies on MIPS assembly code, and requires porting to run on x86 architecture), successor projects have been initiated. In 2004, Stanford University created Pintos, a Nachos-inspired system written in C and designed to run on actual x86 hardware. In 2000, Dan Hettena at UC Berkeley ported Nachos to Java as Nachos 5.0j, in an effort to make Nachos more portable, more accessible to undergraduates, and less susceptible to subtle bugs in student code that had in earlier versions often dominated student project development time. Another Java-based version was created by Professor Peter Druschel at Rice University. It was later adapted by Professor Eugene Stark at Stony Brook University in 2003 and applied in the Operating System course. At Graz University of Technology (Austria), a system called SWEB ("Schon wieder ein Betriebssystem") has been implemented and is used to teach operating system principles.

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References

↑ "Guide to Nachos, University of Pittsburgh" . Retrieved 2014-02-17.
↑ "Compiling C and C++ Programs, University of Wisconsin" . Retrieved 2014-02-17.
↑ "Nachos Beginner's Guide, Level 2: System calls and exceptions, Linköping University" . Retrieved 2014-09-09.
↑ "Machine Class at Nachos Documentation, University of California, Berkeley" . Retrieved 2014-09-09.
↑ "A road map through NachOS, Duke University" . Retrieved 2015-05-05.

External links

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[nachos-1] "Guide to Nachos, University of Pittsburgh" . Retrieved 2014-02-17.

[compiler-2] "Compiling C and C++ Programs, University of Wisconsin" . Retrieved 2014-02-17.

[syscall-3] "Nachos Beginner's Guide, Level 2: System calls and exceptions, Linköping University" . Retrieved 2014-09-09.

[machine-4] "Machine Class at Nachos Documentation, University of California, Berkeley" . Retrieved 2014-09-09.

[Draft_document-5] "A road map through NachOS, Duke University" . Retrieved 2015-05-05.

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