In 1998, Apple introduced HFS Plus to address inefficient allocation of disk space in HFS and to add other improvements. HFS is still supported by current versions of Mac OS, but starting with Mac OS X, an HFS volume cannot be used for booting, and beginning with Mac OS X 10.6 (Snow Leopard), HFS volumes are read-only and cannot be created or updated. In macOS Sierra (10.12), Apple's release notes state that "The HFS Standard filesystem is no longer supported." However, read-only HFS Standard support is still present in Sierra and works as it did in previous versions.