The Limiting Error Correction Capabilities of the CD ROM

Abstract

The purpose of this work was to explore the error correction performance of the CDROM data storage medium in both a standard and hostile environment. A detailed simulation of the channel has been written in Pascal. Using this the performance of the CD-ROM correction strategies against errors may be analysed.Modulated data was corrupted with both burst and random errors. At each stage of the decoding process the remaining errors are both illustrated and discussed. Results are given for a number of varying burst lengths each at different points within the data structure. It is shown that the maximum correctable burst error is approximately 7000 modulated data bytes.The effect of both transient and permanent errors on the performance of a CD-ROM was also investigated. Here software was written which allows both block access times and retries to be obtained from a PC connected to a Hitachi drive unit via a SCSI bus. A number of sequential logical data blocks are read from test discs and access times and retry counts are recorded for each.Results are presented for two classes of disc, one which is clean and one with a surface blemish. Both are exposed to both standard and hostile vibration environments. Three classes of vibration are considered: isolated shock, fixed state sinusoidal and swept sinusoidal. The critical band of frequencies are demonstrated for each level of vibration. The effect of surface errors on the resistance to vibration is investigated.<br/