GeckOS is a discontinued experimental operating system for MOS 6502 and compatible processors.

GeckOS 20.png
GeckOS Shell
DeveloperAndré Fachat
Working stateHistoric
Source modelOpen source
Latest release2.0 / 1999; 20 years ago (1999)
Latest preview2.0.9 / October 6, 2013; 5 years ago (2013-10-06)
PlatformsMOS Technology 6502
Kernel typeMicrokernel


The system offers some Unix-like functionality including preemptive multitasking, multithreading, semaphores, signals, binary relocation, TCP/IP networking via SLIP and a 6502 standard library.

GeckOS includes native support for the Commodore PET (32 KB and 96 KB models), Commodore 64 and the CS/A65 homebrew system. Due to the platform independent nature of the kernel code, GeckOS is advertised as an extremely easy OS to port to alternative 6502 platforms.

Binary compatibility with the LUnix operating system can be attained when the lib6502 shared library is used.

Due to the lack of an MMU and the small fixed-location stack of the 6502, multitasking is somewhat limited. The OS supports a maximum of four tasks when a shared stack space is used. This can be increased to sixteen tasks when stack snapshotting is enabled, although this is done at the expense of some system speed.

External linksEdit