Fudge OS

Jens Nyberg
Project active since
Project active till
Kernel type
User interface
MIT license

Fudge is a small and elegant operating system. It started as a project to see if it would be possible to create an operating system that came as close as possible to be fully deterministic. Today, operating systems often show unpredictable behaviour because they implement technical solutions that are not determinstic in nature such as task scheduling, caching and dynamic memory allocation. Fudge tries to find alternative solutions to these problems and has so far been found to work quite well.

Determinism in the term of computers could mean many different things. It could mean that a program, given input, should always return a conclusive result. However unlikely that sounds it is actually quite common because of unwanted side-effects such as time delays or incorrectly handled input. Determinism could also mean that every time you execute a program it will always take the same amount of time to complete given the same input and the same environment in which it operates.

Fudge focus is on the latter where each programs should complete in the same amount of time or as close as possible. This is not to be confused with a real-time operating system that is only concerned about making sure each task is guaranteed a certain amount of time. Here instead we are concerned with the actual execution time. In order to achieve this Fudge will only run one task at a time and will not interrupt the running task unless an interrupt occurs from hardware or software. This does not mean that Fudge is limited to only run one task at a time because tasks can delay there own execution until such an interrupt occurs and take presedence if the interrupt is of the type it was waiting for. While Fudge operates in kernel mode it can not be interrupted at all so the kernel in that sense is fully deterministic. The kernel also does not keep track of things in a dynamic fashion so each interrupt of the same type should always take the exact same time as any previous. The kernel is not even aware of the fact there can be many tasks running because it can only see the current running one.

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