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Browse Prior Art Database

Transparent Virtual Memory

IP.com Disclosure Number: IPCOM000045004D
Original Publication Date: 1983-Jan-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Barnes, GE: AUTHOR [+3]

Abstract

A method is described whereby a computer may have an optional virtual memory capability that may be installed or removed without modification of the operating system or of application code. The presence and operation of virtual memory is transparent to applications, as well as to the operating system.

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Transparent Virtual Memory

A method is described whereby a computer may have an optional virtual memory capability that may be installed or removed without modification of the operating system or of application code. The presence and operation of virtual memory is transparent to applications, as well as to the operating system.

A simple block diagram of a computer system without virtual memory is shown in Fig. 1 and includes main processor 1 and memory 2. The approach described here is to add virtual memory to such a computer system, as shown in Fig. 2. This system also includes processor 1 and memory 2. However, a Virtual Memory Processor (VMP) 3 is placed between the main processor 1 and physical memory 2.

The job of VMP 3 is to "look like" a very large physical memory to processor
1. The VMP takes cars of how the actual physical memory 2 is used. It may use any scheme (such as paging and/or segmentation) to do its task, and it may do this independently of the programs on the main processor.

Some cooperation is necessary between processors 1 and 3. A simple way to do this is to provide what "looks like" a special I/O device 4 to the main processor. The cooperation occurs as follows.

When the main processor 1 needs to know how much physical memory is available to it, it queries the special I/O device 4. It receives a value corresponding to the physical memory size if VMP 3 is not installed, and it receives a larger value if VMP 3 is present.

When main processor 1 desires to do Direct-Memory Access I/O (DMA I/O), it communicates the starting and ending addresses (or their eq...