--- timing track ------- timing track --- -- 4-bit mark track --- 6-bit mark track bit: 0 1 2 3 0 3 6 9 12 15 4 5 6 7 1 4 7 10 13 16 8 9 10 11 2 5 8 11 14 17 LINCtape Mark track codes: -------------------------- 0000 End Mark 1111 Interblock Mark 1110 Forward Block Mark 0111 Reverse Block Mark 0010 Guard Mark 1001 Data Mark 1011 Final Mark 0001 Check Mark "Forward" tape motion is reversed from DECtape. DECtape Mark track codes: -------------------------- 101101 55 Reverse End Mark 010101 25 Interblock Mark 010110 26 Forward Block Mark 011010 32 Reverse Guard Mark 001000 10 Lock Mark 001000 10 Reverse PCC Mark 001000 10 Reverse Final Mark 001000 10 Reverse Prefinal Mark 111000 70 Data Mark 111011 73 Prefinal Mark 111011 73 Final Mark 111011 73 PCC Mark 111011 73 Reverse Lock Mark 101001 51 Guard Mark 100101 45 Reverse Block Mark 010101 25 Interblock Mark 010010 22 End Mark Two 18 bit words encode three 12 bit words. Blocks are typically 86 18-bit words long, which is to say 129 12-bit words. The symmetry of the DECtape Mark track codes allows reading it in either direction.