Shared memory

Shared memory is the fastest form of Inter-Process Communication (IPC), enabling multiple separate processes to directly access a single, common block of RAM for high-speed data exchange.

This technology bypasses the kernel's typical message-passing overhead, making it the most efficient IPC method available. The operating system kernel initially allocates a specific memory segment, but once established, processes read and write data directly, eliminating costly system calls. For example, a process using POSIX shared memory can map a 4KB page directly into its address space. This speed, however, mandates strict synchronization mechanisms, like semaphores or mutexes, to prevent race conditions and ensure data integrity across the communicating processes.

https://en.wikipedia.org/wiki/Shared_memory