1. Field of the Invention
Example embodiments according to the present general inventive concepts relate to semiconductor memory devices. More particularly, the example embodiments relate to methods of merging blocks in semiconductor memory devices, and semiconductor memory devices that perform methods of merging blocks.
2. Description of the Related Art
Semiconductor memory devices can be roughly divided into volatile memory devices and nonvolatile memory devices according to whether they retain stored data when disconnected from power. Recently, as electronic devices require lower power consumption and smaller size, a NAND flash memory device has been widely used as the nonvolatile memory device. In the NAND flash memory device, a program operation is performed on a page basis, and an erase operation is performed on a block basis.
Generally, since the NAND flash memory device, unlike hard disc drives, does not support an overwrite operation, data modification in the NAND flash memory device should be performed in a manner that programs data of a page to be modified into a free page of the same block or another block with data modification, and assigns an address of the newly programmed page to the modified data by a flash translation layer (FTL). Accordingly, the page that previously stored the data becomes an invalid page, and the page that stores the modified data becomes a valid page. That is, the invalid page may coexist with the valid page in one block.
To obtain free blocks, a block merge operation can be performed by merging valid pages distributed in a plurality of blocks and by erasing unnecessary invalid pages. However, overall performance of the NAND flash memory device may drastically decrease due to the time required to perform the block merge operation.