Glossary · Automation fundamentals, platforms and components
Memory (RAM)
Also known as: Main memory, Work memory, RAM
German: Arbeitsspeicher
In computing and PLCs, memory (RAM, main or work memory) is the fast, usually volatile memory in which a processor holds the program parts and data it is currently executing. In PLCs, the work memory holds the runtime-relevant code and data.
- Automation components
In one sentence
Memory (RAM) is the fast working memory where a processor or PLC holds the code and data it is currently executing.
Example
The PLC's work memory is 85 % full, so the project team moves diagnostic data to a separate controller before adding new functions.
How it applies
- Engineering: Controller selection considers work memory for code and data; many PLCs distinguish work memory from load memory (the stored project) and retentive memory.
- Operation: Volatile memory loses its content on power loss unless data is retentive or backed up.
- Documentation: Technical data should state memory sizes by type. Software documentation should record memory usage and reserve at delivery, which helps plan later extensions.
- Maintenance: Memory upgrades or CPU replacement are sometimes the only way to extend a controller that has run out of memory.
Work memory vs. load memory
Load memory stores the complete project, often on a memory card. Work memory holds the parts needed for execution. Running out of either has different consequences, so the two should not be mixed up in specifications.