Definition
Plain language
A backup that only records what changed since the last save, instead of copying everything again.
As stated in the literature
A snapshotting strategy that stores only the delta from a previous state; used in Firecracker microVMs and in DeltaBox's filesystem and process-memory layers to make checkpoints cheap.
Also called: diff snapshots
Why it matters: Diff snapshots make frequent backups and rollbacks affordable, which is foundational for both VM platforms and modern agent sandboxes.
For example, the first snapshot of a 100GB disk is a full copy, but the next one only records the few megabytes that changed since.
Heard on the show
“The best comparable system before this — Firecracker's diff snapshots — sits at roughly five hundred milliseconds to checkpoint and a second and a half to restore.”Episode 068 — The OS Trick That Makes Tree Search Practical for Coding Agents