Audio Compact Disk - Writing and Reading the data EE 498 Professor Kelin J. Kuhn Two lectures of material Part I A Brief Overview Data storage in CD format is not a simple thing. Typically, a user pictures the "1s" and "0s" in the memory of the computer as being directly transferred to "pits" and "bumps" on the CD disk. Unfortunately, it is far from that easy. To begin with the incoming data is subjected to a series of coding operations. These coding operations add a number of additional parity bits to the data for error detection and correction purposes. The data is also subject to an interleaving process (which means that adjacent data on the disk is not adjacent data from the incoming file). Additionally, the physical form of the data is changed (EFM coding) to eliminate the possibility of adjacent "1s". (This is done because it is the edges of the pit not the pit itself that represent l's in the data stream.) A. Simple error detection and correction codes Error detection and correction codes are fundamental to the operation of any digital storage system. There are literally thousands of such codes. These codes typically rely on using additional bits (usually called parity bits) to carry the error detection and correction information. In a simple binary parity check, a parity bit is a single bit that represents whether the total number of "1s" in a particular data stream is even (1) or odd (0). (Modulo two addition). | |
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