METHOD FOR LOCATING COMPRESSED DATA IN A COMPUTER MEMORY BACKUP DEVICE INCLUDING STEPS OF REFINING ESTIMATED LOCATION

A method for utilizing computer memory devices when they have compressed data is disclosed. Specifically, the techniques focus on the field of operating devices so as to access randomly specified portions of such compressed data. It has particular applicability in computer tape drives such as are used in computer peripheral memory backup devices. These improved methods act to efficiently ascertain the location of the desired data with a minimum amount of effort. One embodiment of the present invention comprises the use of records which represent a number of files or an amount of data stored. Each record is independently compressed to allow independent access and uncompression. The records may include labels for identification purposes. Each label is typically an uncompressed value or series of values stored at the front of each record. Additionally, offsets are specified in labels to indicate the distance from the beginning of the first record to any item of data. The essence of the present invention is to simply calculate an estimated location utilizing an initial compression rate estimate, that is a percentage or ratio that represents the relationship between the average cumulative file size in compressed form of the same data in uncompressed form. Testing this estimate and subsequently refining it serves to efficiently search and retrieve the desired data.