Data storage device, data storage control circuit, and control method for magnetic disk drive

Embodiments of the invention prevent erroneous writing/readout onto/from magnetic disks or other recording disks, even when data transfer between a controller such as an HDC, and a channel such as an R/W channel, and the read/write operation performed by the channel do not match each other in timing. In one embodiment, an HDC/MPU outputs to an R/W channel a starting instruction for data transfer to/from a head, and data that indicates data length of data to be transferred. In response to the data transfer starting instruction from the HDC/MPU, the R/W channel starts transferring, to/from the head, recorded data of the data length notified from the HDC/MPU.