Branches, LCUs, and eKBs

The illustration shows the Windows 10 Vibranium branch and how the latest cumulative updates (LCUs) and enablement packages (eKBs) allow several versions of the Windows client OS to be built from a single, main branch of source code. New security fixes and nonsecurity fixes or updates as well as features for the next version are bundled together into LCU packages which are delivered by Windows Update monthly (middle left of illustration). Over time, a series of LCUs, typically released monthly on Patch Tuesday, are made available for organizations to deploy.

An LCU may contain code for fixes to existing code and code for new or enhanced features (see exploded LCU in the upper left of the illustration). Some new code is delivered by each monthly LCU, but it is marked as disabled so that the new code is installed but not active. This allows the new features to be slowly staged to a device, with the code remaining dormant until all the new code for a new version is present. When Microsoft makes a new version generally available, it provides an enablement package (eKB) to change the status of the new code from disabled to enabled (bottom right of the illustration).