Improving the performance of flash codes using absorption, multibit sub-blocks, and delay of block erasure point



Date of Award


Document Type


Degree Name

Doctor of Philosophy in Computer Science


Information Systems & Computer Science


  • The popularity of flash memory in contemporary computing has led to an upsurge of research in multiple disciplines related to the technology. One important research area focuses on the study of flash code, a specific data encoding and decoding scheme employed in flash memory. This study targets the improvement of flash codes belonging to two different categories, the basic class and the preeminent class, as determined by performance. The de-facto metric called write deficiency (or its normalized form, the write deficiency ratio) is used to quantify the performance of existing and proposed coding schemes. Two new flash codes are presented here. First, the Layered Indexless Indexed Flash Code with Absorption (LILIFCWA) improves on the original idea of the LILIFC. Second, the Multibit Indexless Indexed Flash Code (MBILIFC), based loosely on ILIFC, focuses on high performance. Both LILIFCWA and MBILIFC were envisioned to be competitive with the leading flash codes in both the basic and preeminent classes, respectively. For the basic class, results show significant performance improvements by LILIFCWA over LILIFC in both the average and worst cases. Further, an interesting pattern involving performance impact and degree of bit domination was uncovered. MBILIFC, on the other hand, delivers outstanding performance on the preeminent class, surpassing the Phoenix Flash Code (PFC) for the average case and proves competitive against the latter on the worst case. A third flash code proposed is a hybrid between MBILIFC and the enhanced Binary Indexed Flash Code (BIFC). As of this writing, MBILIFC-EBI provides the lowest known write deficiency ratio for the average case.


The C7.M346 2015