Data compression/decompression apparatus with throttle, start-up and

Abstract

A data compression/decompression apparatus employs common circuitry and a single string table for compression and decompression. A throttle control is provided to prevent data under-runs and an optimizing start-up control delays the start-up of the recording device until the compression apparatus has compressed sufficient data to effeciently reduce throttling and loss of compression when the output device is started. The decompression apparatus may operate to decompress compressed data when the compressed data is read in either the same direction as it was recorded, or read in the direction reverse to that in which it was recorded. A further feature is the provision of a counter which is incremented by one after a predetermined number of string codes have been written into the string table. The output of the counter is stored in the string table with each string code and prefix code. When searching for an empty or usable location in the string table, the count value read from the location is compared with the count in the counter. If the two counts are not equal then the location is considered 'empty' and may be written into. This arrangement avoids the usual procedure of intermittently clearing each location of the string table individually since stepping the counter is equivalent to clearing the entire table.