PUMA
Istituto di Scienza e Tecnologie dell'Informazione     
Lopriore L. Capability based tagged architectures. In: IEEE Transactions on Computers, vol. c-33 (9) pp. 786 - 803. IEEE, 1984.
 
 
Abstract
(English)
An architecture is presented which incorporates capability based addressing and memory tagging features. It defines three kinds of mechanisms for the implementation of object types, which correspond to as many different levels of abstraction. At the lower level, there are the machine types, the operations of which are implemented by machine instructions. At the upper level, there are user types, the operations of which are concretized by means of software routines. The intermediate level is that of predefined types; in this case, too, the operations are supported by software routines, but their efficiency of execution is much greater than is usually to be found in operations of user types. However, one drawback is that these routines should be proved to be correct, as they have a potential for corrupting the integrity of the whole protection system. Each segment of the virtual memory space contains a single object or a machine or predefined type (an object or a user type, on the other hand, is supported by a collection or segments). Besides the segment length and the internal representation of the object, the segment also includes a tag which specifies the type of the object; segments, therefore, represent the basic unit of tagging. The architecture is characterized by interesting performance indexes. In particular, not only does it lead to better memory utilization (as compared to traditional cell-oriented tagged organizations, and even to nontagged environments) but it also allows considerable processing time saving as compared to classical capability architectures (on account of the efficiency with which the operations of predefined types are carried out). Moreover, the facilities for the predefinition of object types make it possible to orient a given machine towards a specific application environment, and are an efficient way of implementing run-time supports for high-level languages.
Subject Abstract Data Type
Abstract Object
Capability
Capability Based Addressing
Object Encapsulation
Segmented Memory
Tagged Architecture
Type Implementation
Type Specification


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