In the automation market, PCs and PLCs are often compared by experts. However, the conclusion is not about which is superior, but rather that each has distinct strengths and directions. In other words, each has its own advantageous applications.

 At one point, innovation in the automation market was centered around the emergence of hardware known as the PLC. Introduced in the late 1960s, the PLC consolidated the complex wiring of relay-based control panels into a single controller that could implement logic. This was revolutionary in many aspects. Based on intuitive ladder logic and programmable via dedicated loaders, PLCs drastically simplified the laborious task of wiring. Since then, PLCs have continuously evolved, expanding their range of control capabilities.

 Meanwhile, computers of the same era—or even earlier—were primarily used for computation. Their main role seemed to be supporting commercial decision-making for businesses. The concept of the PC (Personal Computer), which emerged in the 1970s, rapidly spread across various sectors that required data processing and storage. As such, PCs evolved within the domain of IT (Information Technology), while PLCs grew within OT (Operational Technology), each originating from entirely different fields with distinct purposes.

Figure 1. The Integration of PLC (Control Technology) and PC (Information Technology) in the IT–OT Convergence Process

 The first generation of PLCs introduced in the late 1960s primarily replaced relay control panels for basic on/off control, incorporating logic combinations of input/output and timers/counters. Supported by advancements in technologies such as microprocessors and power electronics, PLCs expanded their control range to include analog signal processing, communications, temperature control, motion control, and more. Over the past six decades, PLCs have undergone significant software and hardware improvements. Moving beyond ladder logic, PLC programming has evolved to include Structured Text (ST), Sequential Function Chart (SFC), Function Block (FB), as well as networking and high-precision motion control. Much of this progress has been achieved by incorporating IT technologies. Concepts once unfamiliar to PLC users—such as User Defined Data Types, Instances, Classes, Arrays, and Aliases—have now become standard. Features traditionally associated with IT, including Web Servers, VNC, and Remote Access, are now embedded within PLCs. In this way, PLCs have made concerted efforts to integrate and connect OT and IT within their control platforms (Figure 1).

Figure 2. Comparison Between PLC Development Environments (e.g., ST Language) and PC Tools (e.g., Visual Studio and C#)

Until just a decade ago, most PLC manufacturers operated conservatively, relying on their solid installed base and loyal customer base. However, it became increasingly difficult to remain competitive using proprietary networks and programming methods alone. Enhancing performance and improving programming efficiency required openness, something that the IT domain excels at—unlike the vendor-dependent environment of traditional PLCs. Adopting IT technologies became a more cost-effective and timely solution than in-house development. One representative example is the adoption of Ethernet-based fieldbus technology. Leveraging IT advancements has enabled PLCs to enhance performance and evolve into more future-proof technologies. In fact, PLCs are increasingly resembling PCs. A clear example of this convergence can be found in the similarities between PLC development environments and PC-based tools like Visual Studio, and between ST (Structured Text) and C# languages (Figure 2). We now see object-oriented programming, efforts toward deterministic execution, modules supporting C languages, direct communication with MES and databases, and even the integration of PC modules into PLCs. Of course, this excludes the PLC’s hardware, often referred to as a stable and robust "black box." Today, referring to a PLC merely as a "Programmable Logic Controller" no longer captures its full capabilities. Hence, the term PAC (Programmable Automation Controller) is increasingly used to reflect the comprehensive nature of modern automation systems.

Currently, PLCs face growing demands to deliver high performance and handle large volumes of data. While they manage considerable amounts of data, real-time data accumulation and analysis remain challenging. The need for data collection and analytics at the equipment level has increased, leading to greater adoption of PCs. This trend is largely driven by the acceleration of Industry 4.0. As a result, it is now common for factory equipment to operate with both PLCs and PCs working in tandem—PLCs for control and PCs for data management.

 

Figure 3. Traditional Control Architecture (PLC + PC) vs. PC-Based Integrated Control System

However, in certain industries, PCs not only handle large-scale data processing but also perform control functions similar to PLCs (Figure 3). A representative example of PC-based integrated control can be found in semiconductor equipment. Nevertheless, PC-based control still holds a very small share of the overall automation market compared to PLCs. This is largely due to PLCs' longstanding optimization for automation, unmatched stability, the high entry barriers for PC control (especially from the perspective of PLC engineers), and concerns over stability and sustainability. Still, one crucial point remains: PCs can indeed control equipment. Just as PLCs have expanded their control domains, PCs have also extended their application scope beyond niche markets. Capabilities once exclusive to PLCs—such as Soft PLC and Soft Motion—are now implementable, and in some cases, even superior on PCs. Several key factors have enabled or accelerated this development: improved PC CPU performance, broader fieldbus coverage (from remote I/O to motion control), enhanced reliability of IPCs, and the adoption of RTOS (Real-Time Operating Systems), as shown in Figure 4.

Figure 4. Ethernet-Based Fieldbus and PC-Based RTOS Technology

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 As PLCs and PCs increasingly cross each other’s boundaries and expand into each other’s domains, we now live in an era where there is significant overlap between the two. From a user’s standpoint, this convergence may not be immediately apparent. In real-world scenarios, it’s rare to find companies or engineers who evaluate both technologies equally or adopt a competitive approach. PLCs and PCs still maintain their own areas of expertise, and existing infrastructure—shaped by industry characteristics, historical momentum, and established supply chains—continues to reinforce traditional approaches. Thus, direct competition between the two technologies remains uncommon.

 

 Nevertheless, the overlapping area between PLCs and PCs will inevitably continue to grow. In the near future, the focus should shift away from the PLC vs. PC debate. Instead, the goal should be to adopt IT technologies more broadly, preserve and embed users’ expertise into the system, and ultimately provide users with sustainable and competitive solutions in the market.

 

- Contributor: Keehoon Kim, CEO of Movensys