Alternatively, modularized, in the sense of one component of a larger system.
For example: In DOS, programs are free to directly diddle a computer's various hardware devices (ports and the like) in any manner they please. In other operating systems (Windows NT for instance), the hardware devices are abstracted, such that they can only be accessed indirectly through the APIs provided by the system. Windows NT uses a Hardware Abstraction Layer (HAL) to accomplish this.
Supposedly this is meant to prevent crashes caused by applications which make improvident use of the hardware, though many NT users would say otherwise.