Why Do ARM Industrial Computers Typically Adopt a 4DI + 4DO Design?

In industrial field applications, an increasing number of users have noticed that whether it's ARM industrial computers, ARM edge controllers, or IIoT gateways, the built-in IO is often configured as 4 digital inputs (DI) + 4 digital outputs (DO). This is no coincidence but a highly engineered consensus formed through the long-term evolution of industrial products.

So, why exactly 4DI + 4DO? What are its limitations? And how can it be overcome?

4DI + 4DO: Covers the Vast Majority of Basic Industrial Control Needs

In practical projects, ARM industrial computers primarily serve as edge data acquisition and linkage control devices, rather than large-scale IO scanning controllers. Typical applications include:

• Water treatment systems
• HVAC / fresh air systems
• Photovoltaic and energy storage EMS
• Remote equipment monitoring
• Cabinet and DCIM systems
• Industrial IoT gateways

Common characteristics of these scenarios:

• Simple control logic
• IO mainly status-based
• Limited number of points

Common IO usages:

DI (Digital Input):

• Equipment run/stop status
• Alarm signals
• Fault feedback
• Interlock signals

DO (Digital Output):

• Start/stop control
• Relay output
• Alarm lights/buzzers
• Valve/motor enable

4DI + 4DO forms a minimal yet complete control loop, meeting over 80% of basic edge control requirements.

4DI + 4DO: The Optimal Balance of Cost and Reliability

Industrial IO is not "the more, the better." Adding each IO channel means:

• Increased optocouplers and isolation components
• Additional TVS, current-limiting, and protection circuits
• Larger PCB area
• Higher EMC/ESD/surge risks
• Elevated certification and testing costs

Long-term industrial design practice has validated 4DI + 4DO as the "sweet spot":

• Fewer than 4: Too functionally limited
• More than 4: Costs rise rapidly, narrowing the target market

Thus, it has become the default configuration for many ARM industrial computers.

ARM Industrial Computers ≠ PLC: IO is Auxiliary, Not Core

A key point: The core strengths of ARM industrial computers lie elsewhere, not in IO point count. Unlike PLCs, they excel in:

• Multi-protocol communication (Modbus/OPC UA/MQTT, etc.)
• Edge computing and data processing
• Web/HMI/Docker/Node-RED
• Local AI inference and data analysis
• Cloud-edge collaboration

IO design principle: "Sufficient is enough; complex IO via expansion." For higher point counts, common approaches include:

• Remote IO
• Modbus IO
• EtherCAT IO
• CANopen IO

Real Limitations of 4DI + 4DO

As project complexity grows, shortcomings emerge:

• Lack of analog AI/AO
• No temperature acquisition (RTD/TC)
• No PWM, encoder, or high-speed IO
• Large project variations in IO types
• Reluctance to repeatedly customize hardware

Fixed IO becomes a bottleneck for rapid deployment.

Beilai Technology ARMxy Series: Breaking the 4DI + 4DO Constraints

Addressing these pain points, Beilai Technology's ARMxy series ARM industrial computers/edge controllers adopt a more flexible IO architecture from the outset.

Supported IO Types (Optional):

• Communication interfaces: RS485/RS232, CAN/CAN FD
• Digital: DI/DO
• Analog: AI/AO
• Temperature: RTD (PT100/PT1000), Thermocouple (TC)
• Control & Expansion: PWM, High-speed IO

Core Advantages:

• Not limited to 4DI + 4DO
• Flexible IO selection per project needs
• No need for per-project hardware customization
• Significantly shortened delivery cycles
• Better suited for multi-industry, multi-scenario solution reuse

Whether in water treatment, energy management, building automation, industrial equipment integration, or edge AI control, the ARMxy series enables rapid adaptation via flexible IO combinations, achieving fast implementation and scalable replication.

Conclusion

4DI + 4DO represents an inevitable stage in the development of ARM industrial computers, but not the endpoint. As demands for flexibility, integration, and delivery efficiency rise, expandable, combinable, multi-type IO edge controllers are becoming the new mainstream. Beilai Technology's ARMxy series is born for this trend.