Why do modern CNC machines still use MS-DOS as the OS?

Question

DOS

By occupation, I often come across various CNC machines, and with a fairly modern fleet. Before, I didn’t think about it, but then something hit my head and thought - in all, without exception, the old MS-DOS is used as the operating system (in some FreeDOS). I don’t understand why manufacturers don’t switch to modern operating systems, say, embedded FreeRTOS or heavier, for example, QNX, or, at worst, some kind of LinuxCNC? What is the mysterious advantage of MS-DOS? .. programmers are probably hard to find now, development environments are obsolete and not supported ...

Answer 1

In the machines we have encountered, the "power" of rtos is simply not required, the control program simply takes over everything - it transfers it from a floppy disk to port 232 and vice versa.
In addition, the processing of existing machines in a modern way does not matter to consumers - they do not work with an operating system.
"It works, don't touch it."

Answer 2

What is the mysterious advantage of MS-DOS?

In the phrase - "works - do not touch." Industrial automation is an ultra-conservative industry, because the price of a mistake is too high. There ISA is still in full use.

Answer 3

In CNC machines, a fairly fast processor is needed (calculation of curved trajectories in a multi-coordinate system), a microcontroller is not suitable for them. Modern ones use Linux on TI Sitara processors, for example.
DOS is somewhat more convenient than FreeRTOS, it allows you to run programs from a file. FreeRTOS is compiled along with the code, it will not be possible to update a separate task, only together with the OS code.