Capability-based addressing

In computer science, capability-based addressing is a scheme used by some computers to control access to memory as an efficient implementation of capability-based security. Under a capability-based addressing scheme, pointers are replaced by protected objects (called capabilities) that can be created only through the use of privileged instructions which may be executed only by either the kernel or some other privileged process authorised to do so. This effectively allows the kernel to control which processes may access which objects in memory without the need to use separate address spaces and therefore requiring a context switch when an access occurs.
Practical implementations.
Two techniques are available for implementation:
The designers of the System/38's descendent systems, including AS/400 and IBM i, removed capability-based addressing. The reason given for this decision is that they could find no way to revoke capabilities (although patterns for implementing revocation in capability systems had been published as early as 1974, even before the introduction of System/38).