Recently I saw a posting on LinkedIn asking “What’s the difference between a SCADA system and an ICS system, and if there is no difference, then why do we have two different names?”

This is a good question, because unless you have worked in the industrial automation field for a few decades, the terminology can seem very confusing. Not only do we have SCADA versus ICS, we also have terms like Process Control, Discrete Control, Industrial Automation, Manufacturing Automation Systems, Distributed Control Systems, Energy Management Systems and so on.

The Quick Answer

Now the quick answer is that Supervisory Control and Data Acquisition (SCADA) is a subset of Industrial Control Systems (ICS).

SCADA generally refers to control systems that span a large geographic area, such as a gas pipeline, power transmission system or water distribution system. I use both terms together because SCADA is often better known by the press, government officials and the public, but ICS is probably the technically correct term to use if you are referring to industrial automation of all types.


Traditionally “SCADA” is used for control systems that cover a wide geographic area. It is also a term that tends to be recognized by the press, government officials and the public.

The History of Industrial Control Led to Many Terms

But to understand why there are so many terms, you need to look back at the history of industrial control, before the days of the micro-controller. In those days a controls practitioner would be involved in one of the following disciplines

 Discipline  Example Industry  Typical Control Equipment

 Process Control


 Distributed Control System


Discrete Control


Programmable Logic Controller


(Wide Area Control)


Master Terminal Unit (MTU) / Remote Terminal Unit (RTU)


Because this was before the micro-controller, there was no PLC, DCS or SCADA equipment as we know it now. Instead process control systems used mechanical pneumatics for logic, discrete control systems used relays and SCADA used transistors and radio. The differences in underlying technologies meant that the systems, the staff, the functionality and the terminologies were all very different.

The Micro-Controller and Convergence

Now along comes the micro-controller and pretty quickly everyone (especially the vendors) realized that the same hardware could theoretically do everything. I say “theoretically” because over the years each vertical had developed a lot of expertise and expectations (and habits) that made it hard to move into another vertical.

For example, as a process engineer in the 1980s, I used to laugh when Allen Bradley would say you can use their PLC-5 for process control because it has a PID controller. Sure that PLC had a PID function block, but it was missing 90% of the features that the process engineers had grown to expect on a DCS. Similarly, trying to do high speed discrete control on a DCS in the 1980s was possible, but a hair pulling exercise. Ditto for using a PLC as a Remote Terminal Unit on a SCADA system; while I never actually tried that, I heard some nasty tales.

Fast forward to today and all the vendors are slowly converging on products that really can move into the other spaces. However there still is a lot of experience and tradition that makes this unlikely. As well, products have been optimized to perform best in a given vertical. So while I probably could use a PLC for controlling a section of refinery, a DCS from a company like Honeywell, Yokogawa, Emerson or Invensys is a more likely choice. 


In the early days of industrial control refineries used the term Distributed Control System or DCS. While DCS is still used today, it is also included in the more comprehensive term “Industrial Control System”.

The Alphabet Soup of Industrial Security Terms

Now in the technology scramble of the last 30 years, many people have debated possible terms that would include all forms of industrial automation. These debates often got very heated.

Some of the suggestions were:

  • Industrial Control System (ICS) - a contender
  • Industrial Automation (IA) – another contender
  • Manufacturing and Control Systems (M&CS) - used by the ISA-99 committees until 2006
  • Industrial Automation and Control Systems (IACS) – now used by the ISA-99 committee
  • Control Systems – too general as it would encompass things like building automation and even home appliances
  • SCADA - as an all-encompassing term, SCADA fails because all us old-timers think of SCADA as wide area control for pipelines, power transmission, etc. (We all wince when someone points to the DCS in a refinery and tries to call it SCADA).

“Industrial Control System” is the Winner

So after hours of debate, many control engineers have now settled on the term "Industrial Control System" (ICS) as the catch-all term. But because ICS is not yet generally known by the layperson, I also use SCADA when I am speaking or writing (of course I also use "SCADA" when I really mean wide area SCADA).

Hopefully this helps. I am sure this debate on terminology is not over yet...

What do you think is the right phrase to describe our industry? Let me know your thoughts and any interesting stories you have on this topic.

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