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System for preventing the use of an unauthorized external memory

  • US 5,134,391 A
  • Filed: 01/08/1990
  • Issued: 07/28/1992
  • Est. Priority Date: 01/10/1989
  • Status: Expired due to Term
First Claim
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1. An authentication system for preventing an unauthorized external memory unit from being used in an information processing system which utilizes a removable external memory unit, said information processing system being capable of displaying a predetermined image by a display means in accordance with a program stored in said external memory unit when the external memory unit is attached thereto, said authentication system comprising:

  • a central processing unit in said information processing system capable of accessing a predetermined maximum address space, an internal memory coupled to said central processing unit having a first memory area corresponding to a first memory space, relatively smaller than said maximum address space, for storing first character data and an authenticity determining program for determining the authenticity of said external memory unit based upon said first character data, and a memory selecting circuit coupled to said internal memory, said central processing unit, and coupled in use to said external memory unit for selecting any one of said internal memory and said external memory unit;

    said external memory unit being coupled in use to said central processing unit and said memory selecting circuit and having an external memory including a second memory area having a memory space corresponding to said first memory space and a third memory area having a relatively larger second memory space;

    said external memory including means for storing second character data having a predetermined relationship with respect to said first character data stored in said internal memory, said second character data being stored in a portion of said third memory area of said external memory, said program stored in said external memory unit for controlling the display of predetermined images and being stored in at least the remaining memory area of said third memory area of said external memory;

    said memory selecting circuit including a first means, responsive to predetermined memory access related signals received from said central processing unit, for selecting said first memory space such that said central processing unit can access said internal memory and a second means for selecting said second memory space such that said central processing unit can access said external memory when the said external memory unit is loaded into said information processing system;

    said central processing unit including means for executing said authenticity determining program for determining whether said first character data which is read from said internal memory and said second character data which is read from said third memory area of said external memory have a predetermined relationship based upon said authenticity determining program stored in said internal memory and for generating an authenticating indicating signal if said predetermined relationship exists;

    wherein said central processing unit includes a display controlling means for controlling the display of said second character data stored in said external memory prior to determining whether said first character data and said second character data have said predetermined relationship, and wherein said memory selecting circuit is responsive to said authenticity indicating signal for selecting said second memory space, whereby said central processing unit can access said program stored in said external memory when said first character data and said second character data have said predetermined relationship.

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