When do WOM codes improve the erasure factor in flash memories?
When do WOM codes improve the erasure factor in flash memories?
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WOM 代码何时可以提高闪存的擦除系数？
DOI：
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
Gala Yadgar
中科院分区：
文献类型：
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作者：
Eitan Yaakobi;Alexander Yucovich;Gal Maor;Gala Yadgar
闪存是一种只写一次的介质，其中重新编程单元需要首先擦除包含它们的块。闪存的寿命是块擦除次数的函数，可以小到几千次。为了减少块擦除的数量，作为最小写入单元的页在存储器中被重写。一次写入存储器（WOM）代码是一种编码方案，其使得能够在擦除之前多次写入块。然而，这些代码具有显著的速率损失。例如，写入两次的速率（具有相同的速率）最多为0.77。在本文中，我们研究WOM码和他们之间的权衡率损失和减少块擦除的数量，当页面均匀随机写入。首先，我们引入了一个新的措施，称为擦除因子，它反映了块擦除的数量和每个块上可以写入的数据量。在我们的分析中的一个关键点是，这种权衡取决于内存中的WOM代码的具体实现。我们考虑两个系统，使用WOM代码，一个传统的计划，通常使用，和一个新的最近的设计，保留了整体的存储容量。虽然第一个系统可以提高擦除因子，只有当存储速率是最多0.6442，我们表明，第二个方案总是提高这个品质因数。
Flash memory is a write-once medium in which re-programming cells requires first erasing the block that contains them. The lifetime of the flash is a function of the number of block erasures and can be as small as several thousands. To reduce the number of block erasures, pages, which are the smallest write unit, are rewritten out-of-place in the memory. A Write-once memory (WOM) code is a coding scheme which enables to write multiple times to the block before an erasure. However, these codes come with significant rate loss. For example, the rate for writing twice (with the same rate) is at most 0.77. In this paper, we study WOM codes and their tradeoff between rate loss and reduction in the number of block erasures, when pages are written uniformly at random. First, we introduce a new measure, called erasure factor, that reflects both the number of block erasures and the amount of data that can be written on each block. A key point in our analysis is that this tradeoff depends upon the specific implementation of WOM codes in the memory. We consider two systems that use WOM codes; a conventional scheme that was commonly used, and a new recent design that preserves the overall storage capacity. While the first system can improve the erasure factor only when the storage rate is at most 0.6442, we show that the second scheme always improves this figure of merit.