1. Field of the Invention
The invention relates to flash memories, and more particularly to strong pages and weak pages of flash memories.
2. Description of the Related Art
Many electronic devices store data with flash memories, such as digital cameras and cell phones. A NAND flash memory comprises a plurality of blocks. Each of the blocks comprises a plurality of pages. Pages are divided into strong pages and weak pages. When data is written to a strong page, the strong page requires a shorter programming period to complete data writing. When data is written to a weak page, the weak page requires a longer programming period to complete data writing.
Referring to FIG. 1, a schematic diagram of a plurality of pages included by a block 100 of a NAND flash memory is shown. The block 100 comprises a plurality of pages. The pages are divided into strong pages and weak pages. For example, pages 0, 1, 2, 3, 6, 7 are strong pages, and pages 4, 5, 8, 9 are weak pages. In addition, a strong page has a corresponding weak page, and a weak page has a corresponding strong page. For example, the strong page 0 corresponds to the weak page 4, the strong page 2 corresponds to the weak page 8, and the strong page 3 corresponds to the weak page 9.
When data is written to a weak page, data stored in a strong page corresponding to the weak page is affected. When data is written to a strong page, data stored in a weak page corresponding to the strong page is also affected. Because a strong page has a shorter programming period, when errors occur in programming of the strong page, a weak page corresponding to the strong page has little probability to suffer from data damage. On the contrary, because a weak page has a longer programming period, when errors occur in programming of the weak page, a strong page corresponding to the weak page will probably suffer from data damage due to data errors of the weak page. A method for securing pages of a flash memory from data damage is therefore required.