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Compared to a standard DVD, Blu-ray's 50GB of storage capacity seems fairly large. Nevertheless, companies have continued to look for ways to squeeze more data onto a single disc. Along with the multi-layer discs developed by Pioneer, Hitachi and TDK, companies are now looking at partial response maximum likelihood (PRML) signal processing as a possible way to store up to 33.4GB of data per single layer. Thanks to Sony and Panasonic, PRML is one step closer to becoming a reality. The two companies recently announced that they've developed a new evaluation technique known as i-MLSE (Maximum Likelihood Sequence Estimation) that can be used to judge the optical quality when reading and writing to 33.4GB media.

Sony and Panasonic Corp. resolved this by developing the i-MLSE (Maximum Likelihood Sequence Estimation) evaluation index. Details of i-MLSE were announced at International Symposium on Optical Memory 2009 (ISOM '09), held in October 2009. The first of the two key characteristics is that i-MLSE has a strong correlation with the error rate (Fig. 1) even in read/write at 33.4 GB using PRML. The second, according to Sony, is that "i-MLSE exhibits the same relationship to signal quality as conventional jitter." In other words, it will be relatively simple to estimate the read error rate from the i-MLSE, just as can be done now with jitter.

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