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Bat algorithm (BA) is one of the promising metaheuristic algorithms. It proved its efficiency in dealing with various optimization problems in diverse fields, such as power and energy systems, economic load dispatch problems, engineering design, image processing and medical applications. Thus, this review introduces a comprehensive and exhaustive review of the BA, as well as evaluates its main characteristics by comparing it with other optimization algorithms. The review paper highlights the performance of BA in different applications and the modifications that have been conducted by researchers (i.e., variants of BA). At the end, the conclusions focus on the current work on BA, highlighting its weaknesses, and suggest possible future research directions. The review paper will be helpful for the researchers and practitioners of BA belonging to a wide range of audiences from the domains of optimization, engineering, medical, data mining and clustering. As well, it is wealthy in research on health, environment and public safety. Also, it will aid those who are interested by providing them with potential future research.

Flash memory-based solid-state drives (SSDs) offer several attractive features and benefits compared to hard disk drive (HDD), such as shock resistance and better performance especially for random data access. Depending on the number of bits in each cell, Flash memory can be designed as single/multi/triple level cell (SLC/MLC/TLC), which have different performance, density, cost and write endurance characteristics. To bring the best of these together, several researchers have proposed designing SSD using hybrid SLC/MLC/TLC Flash memory. However, these SSDs also present several challenges such as buffer management, placement of hot/cold data in suitable portion, and intelligent garbage collection. Several recent techniques aim to address these challenges.In this paper, we present a survey of techniques for managing SSDs designed with SLC/MLC/TLC Flash memory. We classify the works on several axes to bring out their similarities and differences.We aim to synthesize the state-of-art progress in hybrid SSD management and also spark further research in this area. KEYWORDSflash translation layer, garbage collection, hybrid solid state disk, NAND flash memory, wear leveling INTRODUCTIONAs the amount of digital data continues to grow at an exponential rate and key applications become more data intensive, efficient storage architectures and management techniques have become more important than ever before. Conventionally, hard disk drive* has been used as a storage device; however, its limitations such as poor performance (especially for random accesses), higher form factor, and vulnerability to shocks and magnetic fields have encouraged researchers to explore its alternatives.Flash memory is a promising technology for designing storage devices due to its several attractive properties, eg, high performance and density, low power consumption, noise-free operation, and immunity to shocks and magnetic fields. 2-6 Also, its cost has been decreasing in recent years and it is expected to provide even better cost efficiency than HDD in near future. Based on the number of bits stored in each cell, Flash can be characterized as SLC (1 bit), MLC † (2 bit) and TLC (3 bits). As shown in Table 1, these cell types provide a spectrum of properties and trade-offs. Specifically, on going from SLC to MLC to TLC, the performance and write endurance decrease whereas density and cost efficiency improve.To achieve the best of these three cell types, hybrid SSD designs have been proposed, which use Flash memories of multiple cell types to improve performance, energy efficiency, and reliability. 16 However, these hybrid SSD designs also bring challenges, such as selection of relative proportion of SLC/MLC/TLC, efficient mapping/moving of hot/cold data to them, accounting for their disparate write endurance and density values, and

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Due to their high-density and near-zero leakage power consumption, non-volatile memories (NVMs) are promising candidates for designing future memory systems. However, compared to conventional memories, NVMs also face more severe security threats, e.g., the limited write endurance of NVMs makes them vulnerable to write attacks. Also, the nonvolatility of NVMs allows the data to persist even after power-off, which can be accessed by a malicious agent. Further, encryption endangers NVM lifetime and performance by reducing the efficacy of redundant write avoidance techniques. In this paper, we present a survey of techniques for improving security of NVM-based memories by addressing the aforementioned challenges. We highlight the key ideas of the techniques along with their similarities and differences. This paper is expected to be useful for researchers and practitioners in the area of memory and system security.

 Abstract-As a novel storage technology, SSD provide efficient features and challenges. The physical semiconductor characteristics of SSD result into high performance, power consumption, light size, shock resistance, and low noise. With all the benefits of SSD, replacing the conventional HDD drives with pure SSD may not be an efficient option for large-scale storage systems. This is mainly due to many disadvantages of SSD e.g. limited lifespan, small density, and high cost. Thus, a more practical solution is to use hybrid SSD (i.e., SSD consisting of SLC, MLC, and TLC) in hierarchy of storage system, such that the features of this technology are best utilized. In this research, an efficient scheme was proposed. The prosed scheme called Cost, Performance, and Reliability Concern Scheme (CPRCS) for hybrid SSD. CPRCS aim to exploit the trade-off between performance, reliability, cost, density, and power consumption. The eligibility of the CPRCS was proved by using widely used SSD simulation tools: the DiskSim and SSD extension from Microsoft. The results reveal that the proposed scheme is very competitive to state-of-the-art schemes in terms of effectiveness and efficiency.

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