🚀 go-pugleaf

In article <AMPU1411B21767@MPA15AB> MPA15AB!COMPSYSU@TRENGA.tredydev.unisys.com writes:
>> Odd tags indicate that the contents of the memory may not be accessed
>> as normal data.  They do not distinguish whether a word is read-only;
>> a separate bit in the descriptor indicates read-only status.  And
>> even a read-only word can be written to with the overwrite instruction.
>> Odd tags are used for a variety of purposes - e.g., the start and
>> end of arrays in memory, data descriptors, instruction words, IRWs, PCWs.
>> Attempting to access an odd tagged word as data for either reading or
>> writing causes a hardware interrupt.
>

As an aside, there is a discussion of tag field machines (including the
B5500 and B6700 which perhaps A series borrowed or built on?).

	BASIC MACHINE PRINCIPLES
	John K. Iliffe
	Second Edition, 1972
	MACDONALD & CO LTD (UK) ISBN 0 356 03575 1
	AMERICAN ELSEVIER PUBLISHING CO (USA) ISBN 0 444 19582 3

Martin Cryer
UNIX SVR4.0/MP Development
UNISYS Salt Lake City

All opinions are my own and are NOT those of my employer.