Windows Me caches its entire set of compressed cabinet setup files and stores them in the %windir%\Options\Install folder.
WFP covers all files which the operating system installs (such as DLL, EXE, SYS, OCX etc.
WFP integrates with the System File Checker (sfc.exe) utility.
Windows Resource Protection aims to protect core registry keys and values and prevent potentially damaging system configuration changes, besides operating system files.
The non-use of ACLs in Windows File Protection was a design choice: Not only did it allow operation on non-NTFS systems, but it prevented those same "bad" installers from failing completely from a file access error.