Excavating
Patent
1981-10-05
1984-02-28
Atkinson, Charles E.
Excavating
360 53, 364200, 371 13, G06F 1110
Patent
active
044344872
ABSTRACT:
In a disk mass storage facility for data processing systems, a disk format which improves handling of defective segments of medium and reduces access time. The format has three layers. A first, physical layer comprises the bytes, sectors and collections of sectors, as well as error detection and correction codes. A second, logical layer is used to address the physical layer and to collect together sectors to form a multiplicity of separately addressable spaces, with each space having a distinct functional utility. At a third, functional layer the use of data fields in each space is specified. This layer governs the handling of bad blocks if required, and the use of certain format information. Handling of bad blocks is controlled by a hierarchically layered process. A portion of each disc, distributed across the medium, is reserved as spare sectors to replace defective sectors. After a bad sector is replaced, future attempts to access the bad sector are redirected (i.e., revectored) to the replacement sector. For the simplest revectoring, the bad block is replaced by a replacement block in a known location. If that cannot be done, multiple copies of the replacement block's header are stored in the bad block's data field and the copies are compared to find the replacement address. If the comparison fails, or the header cannot be read, a back-up table is available to match the available replacement addresses with the original address which was replaced. A special code is used to identify blocks wherein the medium is good but the contents of the block are logically corrupted.
REFERENCES:
patent: Re31069 (1982-10-01), Chang et al.
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patent: 4037091 (1977-07-01), Beuscher
patent: 4152695 (1979-05-01), Democrate et al.
patent: 4214280 (1980-07-01), Halfhill et al.
Gardner Edward A.
Lary Richard F.
Parenti Mark A.
Rubinson Barry L.
Atkinson Charles E.
Digital Equipment Corporation
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