Memory device with specified write data size

A memory device comprising:

• a nonvolatile memory which stores data in units of a write unit comprising cells;
• and
• a controller which
• controls the nonvolatile memory,
• partitions memory space of the nonvolatile memory,
• in response to a request to write write-data to the nonvolatile memory from a host device, requests the host device to transmit a segment of the write-data with a specified size, wherein the write-data segment has a size determined to allow for a size of a set of part of the write-data segment and corresponding additional data to be the largest while smaller than a size of the write unit, and wherein a size of the part of the write-data segment is a division by an integer of the size of the write-data segment, and
• before completion of processing a first command which requests access to a first partition, accepts a second command which requests access to a second partition.