Questões de Concurso

    Advances in portable computing and Internet service technologies (Byun and Hong, 2000) have resulted in extensive use of portable information devices such as PDAs (Personal Digital Assistants), HPCs (Hand-held PCs), and PPCs (Pocket PCs) in e-commerce environments. Each information device may run several applications, such as a small database, a personal information management system (Greer and Murtaza, 2003), and e-commerce software (Gyeung and Lee, 2003). Flash memory is one of the best candidates to support small information devices for data management in portable computing environments (Byun, 2006).
    Recently, flash memory has become a critical component in building embedded systems or portable devices because it is nonvolatile, shock-resistant, and uses little power. Its performance has improved to a level at which it can be used not only as the main storage for portable computers but also as mass storage for general computing systems (Chang and Kuo, 2005). Although flash memory is not as fast as RAM, it is hundreds of times faster than a hard disk in read operations. These attractive features make flash memory one of the best choices for portable information systems (Yim, 2005).
    However, flash memory has two critical drawbacks. First, a segment, blocks of flash memory, need to be erased before they can be rewritten. This is because flash memory technology only allows individual bits to be toggled in one way for writes. The erase operation writes ones or zeros into all the bits in a segment. This erase operation takes much longer than a read or write operation. The second drawback is that the life of each memory block is limited to 1,000,000 writes. A flash management system should wear down all memory blocks as evenly as possible (Kim and Lee, 1999).
    Due to these disadvantages, traditional database technologies are not easy to apply directly to flash memory databases on portable devices. A database management system which is based on flash memory media must exploit the advantages of flash memory features while overcoming its constraints.

Flash memory shadow paging scheme for portable computers: design and
performance evaluation. In: Journal of Research and Practice in
Information Technology, vol. 39, n.º 3, Aug. 2007 (adapted).

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