What is the memory model in C++11 and how does it affect multithreaded programming?

Hello everyone! I started learning multithreading in C++, and I came across the term "memory model" that appeared in the C++11 standard. Honestly, I don't fully understand what it means and why it's needed.\n\nBefore, I wrote simple single-threaded programs, and it seemed to me that memory was straightforward: variables are stored in RAM, the processor reads and writes them. But when I tried to write a simple example with two threads, I started having strange problems. Here's the code:\n\n```cpp\n#include \n#include \n\nbool flag = false;\nint value = 0;\n\nvoid writer() {\n value = 42;\n flag = true;\n}\n\nvoid reader() {\n while (!flag) {}\n std::cout << "Value: " << value << std::endl;\n}\n\nint main() {\n std::thread t1(writer);\n std::th