Industrial Engineer · phase 4 of 16 · noun
Retentive Memory
Memory configured to preserve selected values through a power cycle or operating-mode change.
The Explain card
- Plain English
- Retentive memory keeps its value through a power cycle. When the controller comes back, the tag is exactly what it was when the lights went out.
- Example
- A production count and the current recipe number are retentive. The line loses power at two in the morning and starts the day with the same count and the same recipe.
- Why it matters
- Whether a value survives an outage is a decision, and the wrong default bites in both directions. A retained step number can restart a sequence mid stroke, and a lost totalizer means a shift's production is gone.
- Hook
- Remembers where it was when the power went out.
Word knowledge
How the word is built, where it came from, and what it sits beside in memory.
In a sentence
The programmer assigns the batch total to retentive memory, then confirms during commissioning that the PLC resumes counting from the recorded value.
Why these words
- retentive Middle English retentif, from Old French and Latin retentivus, retaining adjective identifying the memory's holding characteristic
- memory Middle English memorie, from Old French and Latin memoria, remembrance head noun naming the storage resource
Where it came from
- Origin
- English technical compound of retentive and memory, ultimately from Latin retinere and memoria
- Entered the language
- 20th century
- What changed
- Retentive moved from describing human powers of recall to labeling persistence in technical storage, while memory expanded from recollection to electronic data storage.
How it is spelled
- Pattern
- retentive keeps the adjective ending -ive
- Pattern
- memory ends in consonant plus y and forms the plural memories
- Breaks the pattern
- The related stem is spelled retain in retain but retent- in retentive and retention.
Spelled like
- selective
- protective
- retention
- memories
Broken into chunks
-
re
- retain
- recall
-
tent
- retention
- detention
-
ive
- selective
- protective
-
mem
- memo
- memorial
-
ory
- history
- category
What it sits beside
Same subject
- nonvolatile memory
- battery-backed RAM
- retentive timer
- tag initialization
- first-scan logic
Same shape
- volatile memory
- working memory
- persistent storage
PLC storage classes
- retentive tags
- nonretentive tags
retentive PLC instructions
- retentive timer
- retentive counter
Where it sits in the deck
Phase 4: PLC Memory, Tags, and Instructions
The data a program moves and the instructions that move it, from a single true or false value up to a structured array.
