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Software emulation of bank-switched memory using a virtual DOS monitor and paged memory management

  • US 4,926,322 A
  • Filed: 08/03/1987
  • Issued: 05/15/1990
  • Est. Priority Date: 08/03/1987
  • Status: Expired due to Term
First Claim
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1. A method of operating a computer system, the computer system including a CPU having an address range of greater than 1-Mbyte, a memory having a continuous physical address range of greater than 1-Mbyte, and addressing means connecting said CPU to said memory, comprising the steps of:

  • (a) addressing said memory by said CPU alternatively in;

    a first address mode wherein addresses generated in said CPU are directly used as the physical addresses to access said memory, ora second address mode wherein addresses generated within said CPU are translated using table entries to physical addresses used to access said memory;

    (b) executing an operating system for said CPU stored in said memory using either said first address mode or said second address mode,said operating system defining a user memory area of 0-to-640 Kbyte and a system memory area of 640 Kbyte to 1-Mbyte,said operating system further defining a protocol permitting said CPU to respond to a bank-switched memory access command generated within said CPU by addressing a bank-switched memory system; and

    (c) in response to a said bank-switched memory access command, accessing an extended memory portion of said memory having a continuous physical address range of greater than 1-Mbyte while executing said operating system,said extended memory portion having physical addresses above 1-Mbyte,by operating said addressing means in said second address mode and employing a plurality of said table entries of said addressing means selectively mapped to an expanded memory page frame within said system memory area to access said extended memory portion.

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