Efficient use of flash memory in flash drives

A data storage device having non-volatile solid state memory permits efficient access by permitting multiple pending commands from a host device. A controller in the data storage device stores information about each command from the host device, and determines which stored command, if any, is presently able to be performed based on the portion of the non-volatile memory and the type of access of the command. The data storage device provides reduced access delays, improves read/write throughput, and avoids the cost of additional memory in the data storage device, by allowing accesses to idle portions of memory to proceed, and by signaling the host device when the data storage device is able to accept data to be written to portions of the non-volatile memory already active due to a previous command.