Digital data formatting system for high density magnetic recording

Claim 1

In a system for arranging digital data into records for high density recording on a movable magnetic medium, including; a source of data; generating means for generating a preamble, a postamble and other characters; means for formatting data from said source between said preamble and said postamble and for formatting certain of said other characters with said preamble, said postamble and said data to form each of said records for encoding and recording on said magnetic medium; wherein said preamble and postamble are each comprised of a predetermined number of predetermined characters and said data is comprised of a variable number of characters, said characters each comprised of nine cell positions in which each cell position is adapted to accommodate a flux change signal, the improvement comprising: first means for conditioning said formatting means to insert an unique one of said other characters at the end of said preamble and at the beginning of said postamble, said unique one of said other characters consisting of a cell position containing no flux change signal followed by seven cell positions containing a symmetrical group of flux change signals in turn followed by a cell position containing no flux change signal; second means for conditioning said formatting means to insert a flux change signal in the ninth position of every character in said record, except in the ninth position of said unique one of said other characters, whereby a clocking signal may be derived from at least every tenth cell position in said record and whereby the end of the data contained in a record may be immediately recognized upon reading said unique one of said other characters.