| 摘要 |
PURPOSE:To logically obtain an area protection having various comprehensive relations by constituting a key of plural bits, and also, designating a different protection classification by a value '0' of each bit thereof. CONSTITUTION:A storage key A read out of a key storage device 11, based on an address of an access request is inputted to an area protection control circuit 14 together with a program key B of a program status word (PSW) 13. The area protection control circuit 14 allows each hit (for instance, it is assumed to be 4 bits) of the storage key A and the program key B to correspond to each other, permits an access to a main storage device 12 in the case of A+B=A, and inhibits an access in the case of A+Bnot equal to A. Accordingly, since the key of plural bits is used, a program having an access request to the main storage can have the right of an access by designating plural arbitrary areas having different protection classifications. In such a way, various main storage protections can be realized.
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