multiprocessor

A multiprocessor system contains two or more processing cores or CPUs connected by a shared memory bus and controlled by a single operating system. Unlike a network of separate computers, all processors have direct access to the same RAM and peripherals, allowing them to coordinate work without network overhead. In industrial settings, multiprocessors handle real-time control tasks, high-speed data acquisition, and machine vision processing where latency and synchronization matter.

Multiprocessor architectures fall into two broad classes: symmetric multiprocessing (SMP) and asymmetric multiprocessing (AMP). In SMP systems, all CPUs are identical and any processor can execute any task; the operating system distributes work dynamically across available cores. AMP systems assign specific tasks to specific processors; for example, one core runs the safety-critical control loop while another handles data logging. Industrial equipment often uses AMP when reliability and determinism outweigh flexibility.

Shared Memory and Cache Complexity

The biggest design challenge in multiprocessor systems is cache coherency. When each processor has its own L1 and L2 cache, writes by one processor may not be immediately visible to others. Hardware coherency protocols (such as MESI or MOESI) keep caches synchronized, but this adds latency and power consumption. In real-time industrial applications, cache misses during critical operations can cause timing violations. Some designs use write-through caching or lock-based access to shared data structures to guarantee consistency.

Dual and quad-core processors dominate industrial embedded systems today. A typical industrial PC might use a dual-core Intel Atom or a quad-core ARM Cortex-A processor running a real-time kernel like VxWorks or QNX. Higher core counts (8, 16, or more) appear in vision systems and motion control coordinators, though software engineering complexity grows sharply above four cores.

The term multiprocessor is distinct from multicore. Strictly speaking, a multiprocessor system uses separate CPU chips or discrete processor modules; a multicore system integrates multiple execution units on a single die. In modern industrial terminology, the distinction has blurred, and both configurations are often called multiprocessor. When specifying equipment, clarify whether you need true redundancy (two separate processor modules with independent power supplies) or simply parallel compute capacity on one chip.