ECC : Java Glossary

• Allow you to detect if the message has been garbled.
• Allow you to reconstruct the message if it has not been badly garbled.

Error correcting codes are used in RAM (Random Access Memory), hard disks, DAT (Digital Audio Tape) tapes, CD-ROM (Compact Disc — Read Only Memory)s and rarely in modem transmissions. They are used in some floppy backup programs. I invented an ECC scheme for floppies where the error correction codes were carefully distributed over the disk to avoid irreparable damage from radial or circular scratches and greasy thumbprints. Norton Utilities tried to patent it, but backed down when I challenged them.

Most memory sold now-a-days does not have even error detection logic, much less error correction. When you get an error, the program continues, but with wrong information. This may not be all that important if you are just playing a game, but it could be crucial if you are doing an income tax return. Parity memory is a very simple form of error detection without correction. Because of alpha particle emissions, memory can be expected to make errors every so often, even when it is functioning perfectly.

It may seem like magic, but this will give you the gist of how it works. Imagine I had ten slips of paper each with a number written on them. I made an eleventh slip with the sum of the numbers. I then hand out the slips to people in the audience. Then, at random we select a person and they destroy their slip without showing it to anyone. How would you reconstruct the missing slip from the information on the remaining ten? Hint: add up the remaining slips and compare it with the total.

The actual schemes use much more complicated math than simple addition, but work on the same general principle.