Transport Control Word Non-Contiguous Address List
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Solution Overview
Problem
Current I/O processing systems face limitations in data transfer capacity due to the two-byte count field in Channel Command Words (CCWs), which restricts data transfer to 64 k bytes per operation, and the transport indirect data address list (TIDAL) being confined to a single page, limiting it to 256 entries and one megabyte of data transfer.
Innovation Solution
The introduction of a Transport Control Word (TCW) with a four-byte count field and transport mode indirect data address list (TIDAL) that allows entries to be non-contiguous, enabling more than 256 entries and supporting data transfers of up to four gigabytes within a single I/O operation by using transport mode indirect data address words (TIDAWs) that indicate whether an address is a data address or a continuation address.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the TIDAL is confined to a single page with 256 entries, then the system maintains simple memory management and contiguous address structure, but the data transfer capacity is limited to one megabyte
Solution Approach 1:
The patent divides the TIDAL into multiple pages, with each page containing up to 256 entries. The indirect data address words now include a page number field in addition to the offset, allowing the address list to span multiple memory pages while maintaining the simple 256-entry limit per page. This segmentation enables data transfer capacity to exceed one megabyte while preserving manageable memory structure.
Solution Approach 2:
The patent adds a new dimension to the address structure by incorporating a page number field into the indirect data address words. This transforms the single-page linear structure into a multi-page hierarchical structure, enabling the system to address more than 256 entries without increasing the complexity of individual page management.
2Quantity of substance
If the byte count field in CCW is limited to two bytes, then the CCW structure remains simple, but the data transfer per operation is restricted to 64 k bytes
Solution Approach 1:
The patent changes the byte count field from two bytes to four bytes in the transport control word, increasing the maximum data transfer capacity from 64 k bytes to 4 gigabytes per operation. This parameter change is implemented in the new TCW structure while maintaining backward compatibility with existing systems.
Solution Approach 2:
The patent creates a universal transport control word structure that can handle both small and large data transfers. The four-byte count field provides flexibility to accommodate various data transfer sizes, from small transactions to large bulk transfers, making the system more versatile without requiring multiple specialized control structures.
3Productivity
If multiple exchanges and sequences are used between channel and control unit, then the system maintains compatibility with existing protocols, but communication overhead increases and throughput decreases
Solution Approach 1:
The patent merges multiple CCW operations into a single transport control word that can specify multiple indirect data addresses in one structure. This consolidation reduces the number of separate exchanges and sequences needed between the channel and control unit, decreasing communication overhead and improving I/O throughput while maintaining protocol compatibility.
Solution Approach 2:
The patent performs preliminary setup by organizing multiple data addresses into a single TIDAL structure before the I/O operation begins. This pre-organization allows the channel to process the entire list of addresses in one operation rather than requiring multiple sequential exchanges, reducing communication overhead and improving efficiency.
Data Source
AI summary
A computer program product for processing input/output (I/O) data is provided for performing a method that includes receiving a transport control word (TCW) including an indirect data address including a starting location of a transport mode indirect data address list (TIDAL) of storage addresses, the TIDAL including a plurality of entries configured as transport mode indirect data address words (TIDAWs). The method includes accessing an entry of the TIDAL, which includes: 1) based on the entry of the TIDAL indicating that the address is a data address, gathering data from a data storage location corresponding to the data address, and accessing a next entry of the TIDAL, and 2) based on the entry of the TIDAL indicating that the address is an address of a next entry of the TIDAL, obtaining the next entry of the TIDAL from another storage location that is located non-contiguously to the entry storage location.