Additional data pertaining to the operating system that is external to the data in the ROM itself, which contains the base Newton OS. Newton devices produced by Apple include the Apple ROM Extension (REx) as the initial extension. The Apple REx contains most of the built-in Newton OS applications. For example, on an eMate the REx contains Newton Works. ROM extensions can also define various hardware features, such as system timing, memory specifications, and code.
Clone or licensed Newton OS devices usually include the Apple REx along with a vendor-specific, custom ROM extension.
Up to four ROM extensions can be included on an N2 platform device.