Extremely low error rate digital recording with a helical scan recorder

A low cost, high capacity backup memory is described. The recording mechanism is a modified industrial quality VHS helical scan recorder. Both error avoidance and error correction are used to reduce the error rate to an extremely low level. Error avoidance is accomplished by reading each track after it is written and writing a second copy of any tracks found in error. The read-after-write is done with a high fixed-level threshold to eliminate all tracks with signal dropouts. This gives an uncorrected bit error rate of 10^-9. The error correction code, which can correct a burst of up to 2688 bits, reduces the error rate even further.