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Expanded Key 0 Segment of IBM Series/1 Channel Attachments Translation Table

IP.com Disclosure Number: IPCOM000042108D
Original Publication Date: 1984-Mar-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

Chisholm, DR: AUTHOR [+3]

Abstract

The limits of concurrent I/O operations from device attachments of the IBM Series/1 processor may be greatly expanded by separating Key 0 Translation Table Entries (TTE) from Key 1 through 7 in the Series/1 Channel Attachment. The user of a bus architected (BA) system may view storage as an almost unlimited contiguous virtual space. User I/O requests may map to many non-contiguous pages in real storage, and the I/O handler software must be capable of constructing chains of Device Control Blocks (DCB) pointing to the non-contiguous real pages. Since the present definition of the Series/1 Channel Attachment's translation mechanism provides only 16 TTEs for each Key and Series/1 device attachments must use Key 0 for DCB fetching, the concurrency of Series/1 I/O operations may be severely limited.

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Expanded Key 0 Segment of IBM Series/1 Channel Attachments Translation Table

The limits of concurrent I/O operations from device attachments of the IBM Series/1 processor may be greatly expanded by separating Key 0 Translation Table Entries (TTE) from Key 1 through 7 in the Series/1 Channel Attachment. The user of a bus architected (BA) system may view storage as an almost unlimited contiguous virtual space. User I/O requests may map to many non- contiguous pages in real storage, and the I/O handler software must be capable of constructing chains of Device Control Blocks (DCB) pointing to the non- contiguous real pages. Since the present definition of the Series/1 Channel Attachment's translation mechanism provides only 16 TTEs for each Key and Series/1 device attachments must use Key 0 for DCB fetching, the concurrency of Series/1 I/O operations may be severely limited. Series/1 DCBs are architecturally limited to 16 bytes. By restricting the use of Key 0 to DCB accesses or cycle steal status transfers and using Key 1 through 7 for data transfers, the Key 0 translation mechanism may be expanded and the concurrency of Series/1 I/O operations may be increased. The DCBs could be constructed within a set of unique pages, and since their size is limited, Series/1 I/O could be given logical addresses that translate to the same physical page containing their respective DCBs. With multiple User requests for I/O in a virtual storage system and I/O running translated to r...