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Method for General Sharing of Data in Hybrid Memory Organization

IP.com Disclosure Number: IPCOM000050429D
Original Publication Date: 1982-Oct-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 9 page(s) / 71K

Publishing Venue

IBM

Related People

Matick, RE: AUTHOR

Abstract

This publication describes a simple, hardware implemented means for private or common sharing, or not sharing of data segments in a hybrid memory system. In virtual memory systems, it is desirable to share data segments in some way, either privately or globally. The typical type of sharing is global sharing of COMMON Segments in the MVS operating system. IBM Virtual Machine Facility/370 (VM/370) and, to some extent, TSS (Time Sharing System) provide for private sharing of segments at the segment level. The future operating system MVS/E, while fundamentally providing global "Common" as the main means for sharing, will also incorporate a means to be compatible with VM/370 and TSS. Thus, private as well as common and no sharing of segments at the segment level are desirable and must be provided in a hybrid approach.

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Method for General Sharing of Data in Hybrid Memory Organization

This publication describes a simple, hardware implemented means for private or common sharing, or not sharing of data segments in a hybrid memory system. In virtual memory systems, it is desirable to share data segments in some way, either privately or globally. The typical type of sharing is global sharing of COMMON Segments in the MVS operating system. IBM Virtual Machine Facility/370 (VM/370) and, to some extent, TSS (Time Sharing System) provide for private sharing of segments at the segment level. The future operating system MVS/E, while fundamentally providing global "Common" as the main means for sharing, will also incorporate a means to be compatible with VM/370 and TSS. Thus, private as well as common and no sharing of segments at the segment level are desirable and must be provided in a hybrid approach. We will now outline a simple method for providing this in a hybrid type of main memory organization. A desirable property for private sharing of segments is as follows. If a given segment of virtual name, say, SI(x) (Segment Index x), is declared to the system to be shared by certain specified users, say, STO's a, b, and c, then all these users who wish to share it must call it by the same virtual name (address SI(x)) in their individual virtual address space. If, however, some other user does not want to share that segment, he can still use the same virtual name SI(x) in his address space for some other segment which is not shared. It would also be desirable to allow the same virtual segment name SI(x) to refer to a different segment privately shared by different users, say STO's m, n, and p, if possible. This creates a synonym problem, namely, the same segment name is used to identify different data. However, since the user ID (or STO (Segment Table Origin)) is different and we know ahead of time whether or not the segment is shared, and by which users (this sharing must be initially declared to the system), this private sharing and synonym is easily handled in a hybrid scheme.

There are three cases to be considered, starting with a simple type of sharing and proceeding to the more complex, In the first case, Globally Shared Virtual Space, all shared segments, both COMMON and all private segments, share the same 31-bit virtual address space. In the second case, Semi-Privately Shared Virtual Space, all COMMON resides in one 31-bit virtual space while all privately shared segments fall into a second 31-bit virtual space. In the third case, Privately Shared Virtual Space, COMMON resides in one 31-bit virtual space and all groups of users who are privately sharing segments each have their own 31- bit virtual space. All three of the above cases are implemented by the use of either one or two additional bits in the hybrid associative address register located with each real page, on-chip. In addition, a small Shared Segment Directory implemented in either softwar...