Hard disk drive having buffer memory employing directory based cache controller with data replacement scheme

Claim 1

A disk drive comprising: a recording medium having plural blocks on tracks, each of the blocks being assigned a block address, data being recordable on and retrievable from each block; a buffer memory divided into plural segments each with a capacity for storing at least one block of data; means for recording and retrieving the data on and from the tracks; data processing means for controlling the recording and retrieving means; a buffer memory controller that is separate and apart from the data processing means for temporarily storing one of data read out of the recording medium and data from a host computer in the buffer memory under the control of the data processing means, the buffer memory controller including: first storage means for storing data indicating if valid data are stored in each of the segments; second storage means for storing block addresses of data stored in each of the segments; third storage means for storing block numbers of data stored in each of the segments; fourth storage means for storing information relating to a history of use of data stored in each of the segments; fifth storage means for storing a target block address to be accessed; sixth storage means for storing a block number of the target block to be accessed; segment information selecting means for selecting the first through the fourth storage means corresponding to a specific segment; seventh storage means for storing block hit information indicating that more than one target block specified by the fifth and the sixth storage means have the same block addresses as those of more than one block in the segment specified by the second and the third storage means; means for comparing, under control of the data processing means, block addresses in the segments stored by the second and the third storage means for the segments of which contents are indicated to be valid by the first storage means with the target block addresses stored by the fifth and the sixth storage means and if more than one target block to be accessed as specified by the fifth and the sixth storage means have the same block addresses as those of more than one block in the segments specified by the second and the third storage means, to store the block hit information in the seventh storage means corresponding to this segment; means for updating, under the control of the data processing means, the contents of the fourth storage means to indicate a specific segment most recently accessed for the segments of which contents are indicated to be valid by the first storage means; means for selecting, under the control of the data processing means, the segment to be written based on the contents of the first and the fourth storage means when data are newly stored in any segment of the buffer memory; means for setting, under the control of the data processing means, the contents of the first storage means corresponding to at least one specific segment so as to indicate that the contents of the corresponding segment are invalid; and means for accessing, under the control of the data processing means, at least a predetermined portion of the buffer memory as the corresponding data stored in the recording medium.