Patent
1996-05-20
1997-04-08
Chan, Eddie P.
395461, 395463, 395486, 395487, G06F 1216
Patent
active
056196750
ABSTRACT:
The cache buffer management system functions in a mass storage subsystem to locate a less recently referenced cache buffer to be overwritten with new data. The system of the present invention utilizes P in-cache bitmaps (ICBMs) in a history table to indicate that a particular cache buffer, corresponding to each bit of each ICBM, has been referenced during the past P time periods. A cache buffer is "hot" if the corresponding bit in any of the P ICBMs indicates that the cache buffer has been referenced. Otherwise, where all corresponding bits in all P ICBMs are clear, a cache buffer is "cold". In conjunction with the ICBMs, a track reference count list (TRCL) circular list contains the ID of cache buffers in chronological order of their reference. To determine a buffer suitable for overwriting, the cache buffer management system searches backward from oldest toward newest in the TRCL list of references to find a cache buffer which is "cold". The first "cold" cache buffer found is then overwritten with new data. The combination of ICBMs and the TRCL use less overhead space and uses a memory which comprises a fast portion which may be more rapidly accessed than a remaining slow portion.
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De Martine Patrick A. L.
Milillo Michael S.
Chan Eddie P.
Kim Hong
Storage Technology Corporation
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