frames a preferable solution is to use a frame invariant coding scheme wherein any n grooves in sequence can be decoded into a disk address so that the code rate is 1 0 this is most easily illustrated for the case where each groove codes a single bit but the concept can be extended to two bits per groove or even more it is apparent that a frame invariant code must have the property that adjacent disk addresses share n u2212 1 bits that is the codeword for address x must be a bit shifted version of the codeword for address x 1 fig1 illustrates this for the case n 5 with compound grooves 1501 and pits 1502 1503 1504 here pit x 1503 provides the rightmost address bit for address x 1505 and pit x 1 1504 provides the rightmost address bit for address x 1 1506 the addresses are decoded approaching from the left it is clear however that approaching from the right will simply cause a codeword bit reversal and a remapping of the codewords to the disk addresses frame invariant codes are known in the prior art one such family of codes is based on a linear feedback shift register lfsr 2 http www edatoolscafe com book ch14 ch14 7 htm downloaded jan 22 2002 these devices are used to generate pseudo random bit sequences and to implement finite field math operations consider the three bit lfsr 1601 shown in fig1 the device shown in fig1 produces the pseudo random sequence 7 3 1 4 2 5 6 length 2 3 u2212 1.