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In recent years, flash memory has been widely used in embedded systems, portable devices, and high-performance storage products due to its nonvolatility, shock resistance, low power consumption, and high performance natures. To reduce the product cost, multi-level-cell (MLC) flash memory has been proposed; compared with the traditional single-level-cell (SLC) flash memory that only stores one bit of data per cell, each MLC cell can store two or more bits of data. Thus MLC can achieve a larger capacity and reduce the cost per unit. However, MLC also suffers from the degradation in both performance and reliability. In this paper, we try to enhance the reliability and reduce the product cost of flash-memory-based solid-state drive (SSD) from a totally different perspective. We propose the half-level-cell (HLC) scheme to manage and reuse the worn-out space in SSD; through our management scheme, the system can treat two bad pages as a normal page without sacrificing performance and reliability. The proposed scheme is purely on software/firmware-level, thus there is no need to change the hardware. The experiment results show that the lifetime of SSD with our proposed HLC scheme can be extended to 50.56% under the Windows workload and up to 65.45% under the multimedia workload. When we apply the HLC scheme to flash-memory cache of hybrid storage systems, the response time can be improved up to 20.57%. [ABSTRACT FROM AUTHOR]

Cache vulnerability due to soft errors is one of the reliability concerns in embedded systems. Dynamic reconfiguration techniques are widely studied for improving cache energy without considering the implications of cache vulnerability. Maintaining a useful data longer in the cache can be beneficial for energy improvement due to reduction in miss rates, however, longer data retention negatively impacts the vulnerability due to soft errors. This paper studies the tradeoff between energy efficiency improvement and reduction in cache vulnerability during cache reconfiguration. We propose a heuristic approach for both intertask and intratask cache reconfiguration in multitasking systems. Experimental results demonstrate that our proposed approach can significantly improve both vulnerability (25% on average) and energy efficiency (21% on average) for data cache without violating real-time constraints. [ABSTRACT FROM AUTHOR]