Flash memory has been widely utilized in embedded systems and consumer electronics, because of its low-power consumption, high-performance access, non-volatility, and shock resistance. A flash-memory device is different from a typical hard-disk device and requires a sophisticated management method to improve the reliable endurance and provide the efficient storage management. To improve the reliable endurance and provide the efficient storage management, the previous works have demonstrated that the identification of the frequently used data and the least recently used data is a key point. In this paper, we will propose a hotness filter of files to calculate how the files are accessed (i.e., reads and writes) intensively. The proposed filter is designed specifically to distinguish between hot and cold files by considering the characteristics of file systems. In the experiments, we have implemented the hotness filter in a real Android system (e.g., Asus Nexus 7) and demonstrated that the proposed filter can correctly identify hot and cold files without significant overhead.
Static random access memories (SRAM) are widely used in computer systems and many portable devices. In this paper, we propose an SRAM cell with dual threshold voltage transistors. Low threshold voltage transistors are mainly used in driving bitlines while high threshold voltage transistors are used in latching data voltages. The advantages of dual threshold voltage transistors can be used to reduce the access time and maintain data retention at the same time. Also, the unwanted oscillation of the output bitlines of memories caused by large currents in bitlines is reduced by adding two back-to-back quenchers. The proposed quenchers not only prevent oscillation, but also reduce the idle power consumption when the memory cells are not activated by wordline signals. Meanwhile, a large noise margin is provided such that the gain of the sense amplifier will not be reduced to avoid the oscillation. Hence, high-speed and low-power readout operations of the SRAMs are feasible.
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