RIGOL DS1000D - Manual (Page 21)

Command Systems RIGOL
Programming Guide for DS1000E, DS1000D Series
2-9
The commands set and query the memory depth of the oscilloscope. <depth>
could be LONG (long memory) or NORMal (normal memory)
Returned Format:
The query returns LONG or NORMAL.
Example:
:ACQ:MEMD LONG Set the memory type as LONG.
:ACQ:MEMD? The query returns LONG.