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Enhanced Error Recovery in a Virtually Addressed System Employing Implied Reserve of Real Units

IP.com Disclosure Number: IPCOM000083653D
Original Publication Date: 1975-Jul-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 3 page(s) / 43K

Publishing Venue

IBM

Related People

Waddell, JM: AUTHOR [+3]

Abstract

Common memory apparatus is shared between a plurality of host CPU's, for example, CPU_X and CPU-Y. Each host has its own virtual unit address space which may vary in size from CPU to CPU. Additionally, each CPU has a name for data sets, or virtual volumes, which are "mounted" on the virtual units.

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Enhanced Error Recovery in a Virtually Addressed System Employing Implied Reserve of Real Units

Common memory apparatus is shared between a plurality of host CPU's, for example, CPU_X and CPU-Y. Each host has its own virtual unit address space which may vary in size from CPU to CPU. Additionally, each CPU has a name for data sets, or virtual volumes, which are "mounted" on the virtual units.

When the common memory apparatus receives a MOUNT command from a host CPU, for example, mount virtual volume JJ on virtual unit address X23, tabling entries, not shown, are made relating the host CPU address X23 and virtual volume (VV) JJ. The common memory apparatus then assigns real space, such as shown in the assigned addressed space. For example, on virtual unit X23, real unit A1, address space segments 0-44, and real unit B2, address space segments 20-36, are assigned to the virtual unit.

Similarly, CPU-Y has virtual unit Y014 with a VV of MM mounted on real unit A1, address segments 60-72, and real unit B2, address segments 15-19. Host CPU-Y also shares VV JJ with CPU-X, but appears to host CPU-Y as being on virtual unit Y112. The real address space allocated to the two virtual units X23 and Y112 are the same.

The common memory apparatus also keeps track of which virtual unit currently is active with respect to a real memory unit. The table is called an address using table (AUT). The AUT has one entry for each real memory unit, which shows which CPU and which virtual unit currently is tabled for using the real unit. For example, real unit A1 is being used by CPU-X via virtual unit X23 which would result in an AUT entry for A1 of X23. Similarly, unit B2 may be used by CPU-Y for virtual unit Y014 resulting in an entry of Y014 in the B2 portion of AUT.

Entries in AUT are normally made upon receiving an access command, such as SEEK for a virtual disk memory unit, or SEARCH in a magnetic tape unit. A command chain, using known IBM 360 and 370 channel techniques, maintains the AUT entry. At the end of the chain, the common memory apparatus resets...