Learning from Mistakes: The Therac-25 Code Hazard ⚠️

In the world of building things with tiny computers (we call them embedded systems), even a small mistake in the software can lead to big disasters. Two videos, “History’s Worst Software Error” by Kyle Hill and “How a Simple Bug in Software Ended 6 Lives” by Low Level Learning, tell stories about the Therac-25 mess. These stories are like warnings for engineers, reminding them to be super careful and avoid making the same mistakes.

The Terac 25 Oops

The Therac-25, developed by Atomic Energy of Canada Limited (AECL) in the early 1980s, was a state-of-the-art medical linear accelerator designed to treat cancer patients through radiation therapy. Regarded as a technological marvel, it combined both hardware and software components to deliver precise dosages of radiation. However, a series of catastrophic failures transformed it from a medical marvel to a notorious case study in the world of embedded systems and software engineering.

The Worst Computer Bugs in History: Race conditions in Therac-25

At its core, a software race condition was the primary culprit. This condition occurred when the operator rapidly entered a sequence of commands, causing the software to bypass critical safety checks. The result? The machine would administer a powerful electron beam directly to the patient without the necessary diffusing metal block in place.

The Lessons

1. Testing is Super Important: Before saying a system is good to go, engineers need to test it a lot. They should try out different situations to catch any problems. It’s not just about finishing quickly; it’s about making sure the thing works safely.
2. Think About the People Using It: When making a machine, think about the people using it. The Terac 25 messed up because it didn’t consider how doctors and nurses would interact with it. Engineers need to make things that are easy for people to use and understand.
3. Check Work with Others: Don’t work alone! Engineers should always check each other’s work. This helps catch mistakes early. Also, writing down how things work is crucial, so everyone knows what’s happening.
4. Make Things Safe, Even if Something Goes Wrong: Machines should be made so that even if there’s a mistake, it doesn’t cause big problems. This is called having a backup plan. Terac 25 could have been safer if there were plans to stop it from doing harm when things went wrong.
5. Keep Learning: Technology is always changing. Engineers need to keep learning new things to make sure they’re making safe and good stuff. Learn from mistakes, and always find ways to make things better.

The Therac-25 stories remind engineers to be really careful with their work. Mistakes in tiny computer codes can lead to big problems. So, engineers should test a lot, think about the people using their machines, work together, make things safe, and keep learning. By doing these things, engineers can make sure the things they create are not just cool but also safe and helpful.