Right, but such tools are available across multiple programming languages, and the onus is on Test/QA to ensure that. Lets say that Rust eliminates memory cras

Right, but such tools are available across multiple programming languages, and the onus is on Test/QA to ensure that. Lets say that Rust eliminates memory crashing bugs by restricting certain freedoms afforded by C or C++. The problem of coordinating between multiple threads of who gets to do what when, and with which data and accurately capturing the intent of the programmer still exists. Now if you view the world through Rust-colored glasses, then any invalid state is the result of a programmer error because they used Rust incorrectly. I'm saying that its this the same kind of programmer error (not being able to specify things without ambiguity or a way to capture intent accurately) that was the cause of the memory bug in C too. Its just that with C you will hard crash whereas in Rust you wont. You didn't crash but you modified a data structure you shouldn't have, and your program will still end up in an inconsistent state. In much the same way, the kernel doesn't care what happens in userspace - which thread is doing what with memory or what userspace resources are being corrupted, etc. The kernel can trivially kill userspace threads at will, and continue to remain rock solid as ever. So yes while the separation of kernelmode and usermode helped the user escape from poorly coded apps, it didn't really help reduce the actual bugs as much. Hopefully that made as much sense as it did in my head! :)