In one embodiment of the inventive concept, a partial page program method is provided for a system comprising a nonvolatile memory device. The method comprises loading random data stored in the nonvolatile memory device into a page buffer circuit in the nonvolatile memory device, reloading partial page data having a size corresponding to a portion of one page into the page buffer circuit after the random data is loaded by receiving the partial page data from a memory controller, and programming, to a target page, page data stored in the page buffer circuit after the random data is loaded and the partial page data is reloaded.