Two-phase commit made one transaction span multiple machines by separating preparation from the final decision, but its blocking behavior exposed the cost of making distributed work appear atomic.
The ACID acronym did not invent database transactions, but Theo Härder and Andreas Reuter's 1983 framework gave the field a durable four-part vocabulary—atomicity, consistency, isolation and durability—for discussing transaction guarantees.
IBM's ARIES recovery method combined write-ahead logging, log sequence numbers, repeating history and compensation records into a restart algorithm that could support fine-grained locking and partial rollback.
Jim Gray unified concurrency control, recovery and the transaction abstraction into a framework for keeping shared databases correct even when operations overlap and systems fail.