Jack and Lacuna Debate What “Saved” Means

Afternoon light crossed the desk in Jack’s temporary Petra field room. On the call from Brussels, Lacuna watched him sketch two boxes on a sheet of paper: CACHE and STORAGE.

“Write-back,” Jack said, tapping the first box. “Put the caption change in fast memory, tell me it’s accepted, copy it to storage later. I can keep working instead of waiting for every write.”

“And if the power fails before later?” Lacuna asked. “I want write-through. Every write goes to the cache and the backing store. Don’t tell me it’s done until the durable copy is done.”

“Speed matters when photographs are coming in.”

“So does the name under one.”

Jack leaned forward. “All right. The stored caption says ‘east entrance.’ I change it to ‘west entrance.’ Walk me through the blackout.”

“First: have you actually saved the edit?”

“Not yet.”

“Then neither policy rescues it. If it’s only sitting in the editor’s volatile memory, the new wording can disappear with the power. A cache policy isn’t an automatic Save button.”

Jack drew a small arrow from the caption to the cache. “Now I press Save. The application sends the write. With write-back, this box has ‘west.’ Storage still says ‘east.’”

“And the cache marks that copy as changed—dirty,” Lacuna said. “Assuming an ordinary volatile cache, cut the power before it’s written back and ‘west’ is gone. Restart, read storage: ‘east.’”

“Fast success. Slow regret.” Jack moved his pencil to the second box. “Write-through?”

“Send the change through to storage as well. Once the write is durably completed and acknowledged, a blackout can empty the cache without erasing that saved correction. We reload ‘west’ from storage.”

“Provided storage really commits it, not just another unprotected buffer.”

“Yes. And a failure halfway through isn’t a completed save. I want that distinction on the screen, not buried in a promise.”

Jack looked at the two boxes. “I still want the speed.”

“I still want the caption.”

He underlined STORAGE. “For this path, write-through. We wait for the durable acknowledgment.”

“And until then,” Lacuna said, “the screen says ‘saving,’ not ‘saved.’”