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Hardware Instruction for Indicating Fixed Pages in a Relocatable CPU Environment

IP.com Disclosure Number: IPCOM000077012D
Original Publication Date: 1972-May-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 62K

Publishing Venue

IBM

Related People

Kelley, WJ: AUTHOR [+2]

Abstract

In a relocatable central processing unit (CPU) environment it is often necessary to dynamically designate some blocks of real storage (page frames) as not eligible for being replaced (paged out). This page "fixing" function (and its inverse, "unfixing") can be implemented by a software algorithm that uses this hardware instruction as its key element.

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Hardware Instruction for Indicating Fixed Pages in a Relocatable CPU Environment

In a relocatable central processing unit (CPU) environment it is often necessary to dynamically designate some blocks of real storage (page frames) as not eligible for being replaced (paged out). This page "fixing" function (and its inverse, "unfixing") can be implemented by a software algorithm that uses this hardware instruction as its key element.

The software algorithm requires that a counter be associated with each real- storage page frame to indicate its "fixed" status. Each counter is thus related to a real-storage page frame in a way similar to that of the IBM System/370 storage keys.

During execution of the algorithm, as seen in the drawing, the CPU uses the 8-bit immediate (I2) field of the instruction to increment the counter referenced by the base and displacement (B1 and D1) fields of the instruction. By varying the I2 field, the user varies the effect of the instruction. For example: Immediate (I2) Field Value Effect of Instruction 1 (X'01) Increment counter value by one. 0 (X'00') Test counter value for zero. 255 (X'FF') Decrement counter value by one. (255 is 2's complement form of -1.).

This instruction enables page "fixing" to be done in less than 20% of the time needed by analogous software methods. Testing the "fixed" status of a page requires only two instructions.

Although intended to solve the "fix" problem, this instruction appears to have other uses, such as...