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Abstract: Flash memory is a non-volatile memory which can be electrically erased and reprogrammed. Its major advantages such as small physical size, no mechanical components, low power consumption, and high performance have made it likely to replace the magnetic disk drives in more and more systems. However, flash memory has four specific features which are different to the magnetic disk drives, and pose challenges to develop practical techniques: (1) Flash memory is erased in blocks, but written in pages. (2) A block has to be erased before writing data to the block. (3) A block of flash memory can only be written for a specified number of times. (4) Writing pages within a block should be done sequentially. This survey presents the architectures, technologies, and optimization methods employed by the existing flash memory based storage systems to tackle the challenges. I hope that this paper will encourage researchers to analyze, optimize, and develop practical techniques to improve the performance and reduce the energy consumption of flash memory based storage systems, by leveraging the existing methods and solutions. [Copyright &y& Elsevier]

Abstract: Nowadays, quantum cellular automata (QCA) has been considered as the pioneer technology in next generation computer designs. QCA provides the computer computations at nano level using molecular components as computation units. Although the QCA technology provides smaller chip area and eliminates the spatial constraints than earlier CMOS technology, but different characteristics and design limitations of QCA architectures have led to essential attentions in replacement of traditional structures with QCA ones. Inherent information flow control, limited wire length, and consumed area are of such features and restrictions. In this paper, D flip-flop structure has been considered and we have proposed two new D flip-flop structures which employ the inherent capabilities of QCA in timing and data flow control, rather than ordinary replacement of CMOS elements with equivalent QCA ones. The introduced structures involve small number of cells in contrast to earlier proposed ones in presence of the same or even lower input to output delay. The proposed structures are simulated using the QCADesigner and the validity of them has been proved. [Copyright &y& Elsevier]