In what situations does Apple apply the Copy-on-Write mechanism in its technologies or products?

Apple applies the Copy-on-Write (CoW) mechanism in several key areas to optimize memory usage and improve performance:

• Strings and collections in Swift: Types String, Array, Dictionary in Swift are implemented with CoW. When copying such objects, data is not duplicated immediately, but only upon modification of the copy.

• APFS file system: Uses CoW for file operations and snapshots, allowing efficient creation of instant copies of files without data duplication until modification.

• Virtual memory and processes: When forking a process in macOS and iOS, memory is copied on write — physical copying of pages occurs only upon modification.

This helps save resources and speed up application and system performance overall.