Transaction is a method of coordinating a series of changes to a set of resources distributed over the network. Transactions are units of work that must succeed or fail as a whole - a transaction can never partially succeed.
If a transaction fails while only partially completed, the transaction is rolled back to the beginning. An example is a credit card purchase: The store requests the purchase amount from the credit card company, the company distributes the funds to the store, and the company bills the purchaser.
If any part of the transaction fails, the entire transaction must fail in order to prevent money from being lost.
Component Services on Microsoft Windows 2000 (or Microsoft Transaction Server on Microsoft Windows NT), a tool that provides the underlying support, or “plumbing,” for creating scalable, distributed, transactional Web applications, provides failure isolations and mechanisms for recovering failed transactions and can run components of transactions as isolated processes for additional crash protection. Component Services uses the Distributed Component Object Model (DCOM) programming architecture for communication between components on Microsoft Windows networks.